## 100 Package trigtools ¶

# Trigtools Package

Aleksas Dormarkas
aleksasd873@gmail.com
aleksas.domarkas@mif.vu.lt
December 1, 2013

### 100.1 Introduction to trigtools ¶

We use open-source computer algebra system(CAS) maxima 5.31.2. The trigtools package10 contains commands that help you work with trigonometric expressions. List of functions in trigtools package:

- `c2sin`
- `c2cos`
- `c2trig`
- `c2hyp`
- `trigfactor`
- `trigsolve`
- `trigvalue`
- `trigeval`
- `atan_contract`

Categories: Trigonometric functions · Package trigtools ·

### 100.2 Functions and Variables for trigtools ¶

#### 100.2.1 Convert to sin and cos ¶

Function: c2sin (x) ¶
Function: c2cos (x) ¶

  The function c2sin converts the expression \(a\cos x + b\sin x\) to \(r\sin(x+\phi).\)

  The function c2cos converts the expression \(a\cos x + b\sin x\) to \(r\cos(x-\phi).\)

  `load("trigtools")` loads these functions.

  Examples:

      (%i1) load("trigtools")$

      (%i2) c2sin(3*sin(x)+4*cos(x));
                                            4
      (%o2)                  5 sin(x + atan(-))
                                            3

      (%i3) trigexpand(%),expand;
      (%o3)                  3 sin(x) + 4 cos(x)

      (%i4) c2cos(3*sin(x)-4*cos(x));
                                             3
      (%o4)                 - 5 cos(x + atan(-))
                                             4

      (%i5) trigexpand(%),expand;
      (%o5)                  3 sin(x) - 4 cos(x)

      (%i6) c2sin(sin(x)+cos(x));
                                            %pi
      (%o6)                 sqrt(2) sin(x + ---)
                                             4

      (%i7) trigexpand(%),expand;
      (%o7)                    sin(x) + cos(x)

      (%i8) c2cos(sin(x)+cos(x));
                                            %pi
      (%o8)                 sqrt(2) cos(x - ---)
                                             4

      (%i9) trigexpand(%),expand;
      (%o9)                    sin(x) + cos(x)

  Example. Solve trigonometric equation

      (%i1) eq:3*sin(x)+4*cos(x)=2;
      (%o1)                3 sin(x) + 4 cos(x) = 2

      (%i2) plot2d([3*sin(x)+4*cos(x),2],[x,-%pi,%pi]);
      (%o2)                         false

      (%i1) load("trigtools")$
      (%i2) eq:3*sin(x)+4*cos(x)=2$

      (%i3) eq1:c2sin(lhs(eq))=2;
                                          4
      (%o3)                5 sin(x + atan(-)) = 2
                                          3

      (%i4) solvetrigwarn:false$

      (%i5) solve(eq1)[1]$ x1:rhs(%);
                                   2         4
      (%o6)                   asin(-) - atan(-)
                                   5         3

      (%i7) float(%), numer;
      (%o7)                 - 0.5157783719341241

      (%i8) eq2:c2cos(lhs(eq))=2;
                                          3
      (%o8)                5 cos(x - atan(-)) = 2
                                          4

      (%i9) solve(eq2,x)[1]$ x2:rhs(%);
                                   3         2
      (%o10)                  atan(-) + acos(-)
                                   4         5

      (%i11) float(%), numer;
      (%o11)                  1.802780589520693

      (%i12) sol:[x1,x2];
                         2         4        3         2
      (%o12)       [asin(-) - atan(-), atan(-) + acos(-)]
                         5         3        4         5

  Answ.: \(x = x_1 + 2\pi k,\) \(x_1 = \sin^{-1}{2\over 5} - \tan^{-1}{4\over 3},\) or \(x_1 = \tan^{-1}{3\over 4} + \cos^{-1}{2\over 5},\) for \(k\) any integer.

  Categories: Trigonometric functions · Hyperbolic functions · Package trigtools ·

#### 100.2.2 Convert to Trigonometric Functions ¶

Function: c2trig (x) ¶

  The function c2trig (convert to trigonometric) reduce expression with hyperbolic functions sinh, cosh, tanh, coth to trigonometric expression with sin, cos, tan, cot.

  `load("trigtools")` loads these functions.

  Examples:

  1.     (%i1) load(trigtools)$

         (%i2) sinh(x)=c2trig(sinh(x));
         (%o2)               sinh(x) = - %i sin(%i x)

         (%i3) cosh(x)=c2trig(cosh(x));
         (%o3)                  cosh(x) = cos(%i x)

         (%i4) tanh(x)=c2trig(tanh(x));
         (%o4)               tanh(x) = - %i tan(%i x)

         (%i5) coth(x)=c2trig(coth(x));
         (%o5)                coth(x) = %i cot(%i x)

  2. see https://maxima.sourceforge.io/ext/list_archives/2013/msg03230.html

         (%i1) load("trigtools")$

         (%i2) cos(p+q*%i);
         (%o2)                     cos(%i q + p)

         (%i3) trigexpand(%);
         (%o3)          cos(p) cosh(q) - %i sin(p) sinh(q)

         (%i4) c2trig(%);
         (%o4)                     cos(%i q + p)

  3.     (%i1) load("trigtools")$

         (%i2) sin(a+b*%i);
         (%o2)                     sin(%i b + a)

         (%i3) trigexpand(%);
         (%o3)          %i cos(a) sinh(b) + sin(a) cosh(b)

         (%i4) c2trig(%);
         (%o4)                     sin(%i b + a)

  4.     (%i1) load("trigtools")$

         (%i2) cos(a*%i+b*%i);
         (%o2)                   cos(%i b + %i a)

         (%i3) trigexpand(%);
         (%o3)           sinh(a) sinh(b) + cosh(a) cosh(b)

         (%i4) c2trig(%);
         (%o4)                   cos(%i b + %i a)

  5.     (%i1) load("trigtools")$

         (%i2) tan(a+%i*b);
         (%o2)                     tan(%i b + a)

         (%i3) trigexpand(%);
                                %i tanh(b) + tan(a)
         (%o3)                 ---------------------
                               1 - %i tan(a) tanh(b)

         (%i4) c2trig(%);
         (%o4)                     tan(%i b + a)

  6.     (%i1) load("trigtools")$

         (%i2) cot(x+%i*y);
         (%o2)                     cot(%i y + x)

         (%i3) trigexpand(%);
                              - %i cot(x) coth(y) - 1
         (%o3)                -----------------------
                                cot(x) - %i coth(y)

         (%i4) c2trig(%);
         (%o4)                     cot(%i y + x)

  Categories: Trigonometric functions · Package trigtools ·

#### 100.2.3 Convert to Hyperbolic Functions ¶

Function: c2hyp (x) ¶

  The function c2hyp (convert to hyperbolic) convert expression with exp function to expression with hyperbolic functions sinh, cosh.

  `load("trigtools")` loads this function.

  Examples:

      (%i1) load("trigtools")$

      (%i2) c2hyp(exp(x));
      (%o2)                   sinh(x) + cosh(x)

      (%i3) c2hyp(exp(x)+exp(x^2)+1);
                       2          2
      (%o3)      sinh(x ) + cosh(x ) + sinh(x) + cosh(x) + 1

      (%i4) c2hyp(exp(x)/(2*exp(y)-3*exp(z)));
                              sinh(x) + cosh(x)
      (%o4)     ---------------------------------------------
                2 (sinh(y) + cosh(y)) - 3 (sinh(z) + cosh(z))

  Categories: Trigonometric functions · Hyperbolic functions · Package trigtools ·

#### 100.2.4 Factor Sums of sin and cos Functions ¶

Function: trigfactor (x) ¶

  The function trigfactor factors expressions of form \(\pm \sin x \pm \cos y.\)

  `load("trigtools")` loads this function.

  Examples:

  1.     (%i1) load("trigtools")$

         (%i2) trigfactor(sin(x)+cos(x));
                                               %pi
         (%o2)                 sqrt(2) cos(x - ---)
                                                4

         (%i3) trigrat(%);
         (%o3)                    sin(x) + cos(x)

  2.     (%i1) load("trigtools")$

         (%i2) trigfactor(sin(x)+cos(y));
                              y   x   %pi      y   x   %pi
         (%o2)          2 cos(- - - + ---) cos(- + - - ---)
                              2   2    4       2   2    4

         (%i3) trigrat(%);
         (%o3)                    cos(y) + sin(x)

  3.     (%i1) load("trigtools")$

         (%i2) trigfactor(sin(x)-cos(3*y));
                            3 y   x   %pi      3 y   x   %pi
         (%o2)        2 sin(--- - - + ---) sin(--- + - - ---)
                             2    2    4        2    2    4

         (%i3) trigrat(%);
         (%o3)                   sin(x) - cos(3 y)

  4.     (%i1) load("trigtools")$

         (%i2) trigfactor(-sin(5*x)-cos(3*y));
                           3 y   5 x   %pi      3 y   5 x   %pi
         (%o2)     - 2 cos(--- - --- + ---) cos(--- + --- - ---)
                            2     2     4        2     2     4

         (%i3) trigrat(%);
         (%o3)                 - cos(3 y) - sin(5 x)

  5.     (%i1) load("trigtools")$

         (%i2) sin(alpha)+sin(beta)=trigfactor(sin(alpha)+sin(beta));
                                              beta   alpha
         (%o2) sin(beta) + sin(alpha) = 2 cos(---- - -----)
                                               2       2
                                                             beta   alpha
                                                         sin(---- + -----)
                                                              2       2

         (%i3) trigrat(%);
         (%o3)    sin(beta) + sin(alpha) = sin(beta) + sin(alpha)

  6.     (%i1) load("trigtools")$

         (%i2) sin(alpha)-sin(beta)=trigfactor(sin(alpha)-sin(beta));
                                                beta   alpha
         (%o2) sin(alpha) - sin(beta) = - 2 sin(---- - -----)
                                                 2       2
                                                             beta   alpha
                                                         cos(---- + -----)
                                                              2       2

  7.     (%i1) load("trigtools")$

         (%i2) cos(alpha)+cos(beta)=trigfactor(cos(alpha)+cos(beta));
                                              beta   alpha
         (%o2) cos(beta) + cos(alpha) = 2 cos(---- - -----)
                                               2       2
                                                             beta   alpha
                                                         cos(---- + -----)
                                                              2       2

  8.     (%i1) load("trigtools")$

         (%i2) cos(alpha)-cos(beta)=trigfactor(cos(alpha)-cos(beta));
                                              beta   alpha
         (%o2) cos(alpha) - cos(beta) = 2 sin(---- - -----)
                                               2       2
                                                             beta   alpha
                                                         sin(---- + -----)
                                                              2       2

  9.     (%i1) load("trigtools")$

         (%i2) trigfactor(3*sin(x)+7*cos(x));
         (%o2)                  3 sin(x) + 7 cos(x)

         (%i3) c2sin(%);
                                                   7
         (%o3)               sqrt(58) sin(x + atan(-))
                                                   3

         (%i4) trigexpand(%),expand;
         (%o4)                  3 sin(x) + 7 cos(x)

  10.     (%i1) load("trigtools")$

          (%i2) trigfactor(sin(2*x));
          (%o2)                       sin(2 x)

          (%i3) trigexpand(%);
          (%o3)                    2 cos(x) sin(x)

  Categories: Trigonometric functions · Package trigtools ·

#### 100.2.5 Solve Trigonometric Equations ¶

Function: trigsolve (x) ¶

  The function trigsolve find solutions of trigonometric equation from interval \([a,b).\)

  `load("trigtools")` loads this function.

  Examples:

  1.     (%i1) eq:eq:3*sin(x)+4*cos(x)=2;
         (%o1)                3 sin(x) + 4 cos(x) = 2

         (%i2) plot2d([3*sin(x)+4*cos(x),2],[x,-%pi,%pi]);
         (%o2)                         false

         (%i1) load("trigtools")$
         (%i2) eq:eq:3*sin(x)+4*cos(x)=2$

         (%i3) sol:trigsolve(eq,-%pi,%pi);
                     2 sqrt(21)   12              2 sqrt(21)   12
         (%o3) {atan(---------- - --), %pi - atan(---------- + --)}
                         5        5                   5        5

         (%i4) float(%), numer;
         (%o4)      {- 0.5157783719341241, 1.8027805895206928}

     Answ. : \(x = \tan^{-1}\left({2\sqrt{21}\over 5} - {12\over 5}\right) + 2\pi k\) ; \(x = \pi - \tan^{-1}\left({2\sqrt{21}\over 5} + {12\over 5}\right) + 2\pi k,\) \(k\) – any integer.

  2.     (%i1) load("trigtools")$

         (%i2) eq:cos(3*x)-sin(x)=sqrt(3)*(cos(x)-sin(3*x));
         (%o2)    cos(3 x) - sin(x) = sqrt(3) (cos(x) - sin(3 x))

         (%i3) plot2d([lhs(eq)-rhs(eq)], [x,0,2*%pi])$

     We have 6 solutions from [0, 2*pi].

         (%i1) load("trigtools")$
         (%i2) eq:cos(3*x)-sin(x)=sqrt(3)*(cos(x)-sin(3*x))$
         (%i3) plot2d([lhs(eq)-rhs(eq)], [x,0.2,0.5])$

         (%i1) load("trigtools")$
         (%i2) load("trigtools")$
         (%i3) eq:cos(3*x)-sin(x)=sqrt(3)*(cos(x)-sin(3*x))$
         (%i4) plot2d([lhs(eq)-rhs(eq)], [x,3.3,3.6])$

         (%i1) load("trigtools")$
         (%i2) eq:cos(3*x)-sin(x)=sqrt(3)*(cos(x)-sin(3*x))$

         (%i3) trigfactor(lhs(eq))=map(trigfactor,rhs(eq));
                           %pi            %pi
         (%o3) - 2 sin(x + ---) sin(2 x - ---) =
                            4              4
                                                       %pi            %pi
                                     2 sqrt(3) sin(x - ---) sin(2 x - ---)
                                                        4              4

         (%i4) factor(lhs(%)-rhs(%));
                        4 x + %pi                4 x - %pi
         (%o4) - 2 (sin(---------) + sqrt(3) sin(---------))
                            4                        4
                                                                8 x - %pi
                                                            sin(---------)
                                                                    4

     Equation is equivalent to

         (%i1) load("trigtools")$
         (%i2) eq:cos(3*x)-sin(x)=sqrt(3)*(cos(x)-sin(3*x))$

         (%i3) trigfactor(lhs(eq))=map(trigfactor,rhs(eq));
                           %pi            %pi
         (%o3) - 2 sin(x + ---) sin(2 x - ---) =
                            4              4
                                                       %pi            %pi
                                     2 sqrt(3) sin(x - ---) sin(2 x - ---)
                                                        4              4

         (%i4) L:factor(rhs(%)-lhs(%));
                      4 x + %pi                4 x - %pi       8 x - %pi
         (%o4) 2 (sin(---------) + sqrt(3) sin(---------)) sin(---------)
                          4                        4               4

         (%i5) eq1:part(L,2)=0;
                        4 x + %pi                4 x - %pi
         (%o5)      sin(---------) + sqrt(3) sin(---------) = 0
                            4                        4

         (%i6) eq2:part(L,3)=0;
                                    8 x - %pi
         (%o6)                  sin(---------) = 0
                                        4

         (%i7) S1:trigsolve(eq1,0,2*%pi);
                                    %pi  13 %pi
         (%o7)                     {---, ------}
                                    12     12

         (%i8) S2:trigsolve(eq2,0,2*%pi);
                             %pi  5 %pi  9 %pi  13 %pi
         (%o8)              {---, -----, -----, ------}
                              8     8      8      8

         (%i9) S:listify(union(S1,S2));
                      %pi  %pi  5 %pi  13 %pi  9 %pi  13 %pi
         (%o9)       [---, ---, -----, ------, -----, ------]
                      12    8     8      12      8      8

         (%i10) float(%), numer;
         (%o10) [0.2617993877991494, 0.39269908169872414,
         1.9634954084936207, 3.4033920413889422, 3.5342917352885173,
         5.105088062083414]

     Answer: \(x = a + 2\pi k,\) where \(a\) any from \(S\), \(k\) any integer.

  3.     (%i1) load("trigtools")$

         (%i2) eq:8*cos(x)*cos(4*x)*cos(5*x)-1=0;
         (%o2)          8 cos(x) cos(4 x) cos(5 x) - 1 = 0

         (%i3) trigrat(%);
         (%o3)     2 cos(10 x) + 2 cos(8 x) + 2 cos(2 x) + 1 = 0

     Left side is periodic with period \(T=\pi.\)

     We have 10 solutions from [0, pi].

         (%i1) load("trigtools")$
         (%i2) eq:8*cos(x)*cos(4*x)*cos(5*x)-1=0$

         (%i3) plot2d([lhs(eq),rhs(eq)],[x,0,%pi]);
         (%o3)                         false

         (%i1) load("trigtools")$
         (%i2) eq:8*cos(x)*cos(4*x)*cos(5*x)-1=0$

         (%i3) x4:find_root(eq, x, 1.3, 1.32);
         (%o3)                  1.3089969389957472

         (%i4) x5:find_root(eq, x, 1.32, 1.35);
         (%o4)                  1.3463968515384828

         (%i5) plot2d([lhs(eq),0], [x,1.3,1.35], [gnuplot_preamble, "set grid;"]);
         (%o5)                         false

     Equation we multiply by \(2\sin x\cos 2x:\)

         (%i1) load("trigtools")$
         (%i2) eq:8*cos(x)*cos(4*x)*cos(5*x)-1=0$

         (%i3) eq*2*sin(x)*cos(2*x);
         (%o3) 2 sin(x) cos(2 x) (8 cos(x) cos(4 x) cos(5 x) - 1) = 0

         (%i4) eq1:trigreduce(%),expand;
         (%o4)                sin(13 x) + sin(x) = 0

         (%i5) trigfactor(lhs(eq1))=0;
         (%o5)                2 cos(6 x) sin(7 x) = 0

         (%i6) S1:trigsolve(cos(6*x),0,%pi);
                       %pi  %pi  5 %pi  7 %pi  3 %pi  11 %pi
         (%o6)        {---, ---, -----, -----, -----, ------}
                       12    4    12     12      4      12

         (%i7) S2:trigsolve(sin(7*x),0,%pi);
                        %pi  2 %pi  3 %pi  4 %pi  5 %pi  6 %pi
         (%o7)      {0, ---, -----, -----, -----, -----, -----}
                         7     7      7      7      7      7

     We remove solutions of \(\sin x = 0\) and \(\cos 2x = 0.\)

         (%i1) load("trigtools")$
         (%i2) S1:trigsolve(cos(6*x),0,%pi)$
         (%i3) S2:trigsolve(sin(7*x),0,%pi)$

         (%i4) S3:trigsolve(sin(x),0,%pi);
         (%o4)                          {0}

         (%i5) S4:trigsolve(cos(2*x),0,%pi);
                                    %pi  3 %pi
         (%o5)                     {---, -----}
                                     4     4

     We find 10 solutions from \([0, \pi]:\)

         (%i1) load("trigtools")$
         (%i2) S1:trigsolve(cos(6*x),0,%pi)$
         (%i3) S2:trigsolve(sin(7*x),0,%pi)$
         (%i4) S3:trigsolve(sin(x),0,%pi)$
         (%i5) S4:trigsolve(cos(2*x),0,%pi)$

         (%i6) union(S1,S2)$ setdifference(%,S3)$ setdifference(%,S4);
                %pi  %pi  2 %pi  5 %pi  3 %pi  4 %pi  7 %pi  5 %pi
         (%o8) {---, ---, -----, -----, -----, -----, -----, -----,
                12    7     7     12      7      7     12      7
                                                            6 %pi  11 %pi
                                                            -----, ------}
                                                              7      12

         (%i9) S:listify(%);
                %pi  %pi  2 %pi  5 %pi  3 %pi  4 %pi  7 %pi  5 %pi
         (%o9) [---, ---, -----, -----, -----, -----, -----, -----,
                12    7     7     12      7      7     12      7
                                                            6 %pi  11 %pi
                                                            -----, ------]
                                                              7      12

         (%i10) length(S);
         (%o10)                         10

         (%i11) float(S), numer;
         (%o11) [0.2617993877991494, 0.4487989505128276,
         0.8975979010256552, 1.3089969389957472, 1.3463968515384828,
         1.7951958020513104, 1.8325957145940461, 2.243994752564138,
         2.6927937030769655, 2.8797932657906435]

     Answer: \(x = a + 2\pi k,\) where \(a\) any from \(S\), \(k\) any integer.

  Categories: Trigonometric functions · Package trigtools ·

#### 100.2.6 Evaluation of Trigonometric Functions ¶

Function: trigvalue (x) ¶

  The function trigvalue compute values of \(\sin {m\pi\over n},\) \(\cos {m\pi\over n},\) \(\tan {m\pi\over n},\) and \(\cot {m\pi\over n}\) in radicals.

  `trigvalue` is essentially an internal function. Use function `trigeval` in preference.

  `load("trigtools")` loads this function.

Function: trigeval (x) ¶

  The function trigeval compute values of expressions with \(\sin {m\pi\over n},\) \(\cos {m\pi\over n},\) \(\tan {m\pi\over n},\) and \(\cot {m\pi\over n}\) in radicals.

`load("trigtools")` loads this function.

Examples:

1. Values of trigonometric functions

       (%i1) load("trigtools")$
       (%i2) load(trigtools)$

       (%i3) trigvalue(sin(%pi/10));
                                  sqrt(5) - 1
       (%o3)                      -----------
                                       4

       (%i4) trigvalue(cos(%pi/10));
                               sqrt(sqrt(5) + 5)
       (%o4)                   -----------------
                                      3/2
                                     2

       (%i5) trigvalue(tan(%pi/10));
                              sqrt(5 - 2 sqrt(5))
       (%o5)                  -------------------
                                    sqrt(5)

       (%i6) float(%), numer;
       (%o6)                  0.3249196962329063

       (%i7) float(tan(%pi/10)), numer;
       (%o7)                  0.3249196962329063

       (%i8) trigvalue(cot(%pi/10));
       (%o8)                  sqrt(2 sqrt(5) + 5)

       (%i9) float(%), numer;
       (%o9)                  3.0776835371752536

       (%i10) float(cot(%pi/10)), numer;
       (%o10)                  3.077683537175254

       (%i11) trigvalue(sin(%pi/32));
                     sqrt(2 - sqrt(sqrt(sqrt(2) + 2) + 2))
       (%o11)        -------------------------------------
                                       2

       (%i12) trigvalue(cos(%pi/32));
                     sqrt(sqrt(sqrt(sqrt(2) + 2) + 2) + 2)
       (%o12)        -------------------------------------
                                       2

       (%i13) trigvalue(cos(%pi/256));
       (%o13) sqrt(sqrt(sqrt(sqrt(sqrt(sqrt(sqrt(2) + 2) + 2) + 2) + 2)
                                                             + 2) + 2)/2

       (%i14) trigvalue(cos(%pi/60));
       (%o14)
         sqrt(sqrt(sqrt(2) sqrt(3) sqrt(sqrt(5) + 5) + sqrt(5) + 7) + 4)
         ---------------------------------------------------------------
                                       3/2
                                      2

       (%i15) trigvalue(sin(%pi/60));
       (%o15)
         sqrt(4 - sqrt(sqrt(2) sqrt(3) sqrt(sqrt(5) + 5) + sqrt(5) + 7))
         ---------------------------------------------------------------
                                       3/2
                                      2

       (%i16) trigvalue(sin(%pi/18));
                                       %pi
       (%o16)                      sin(---)
                                       18

       (%i17) trigvalue(sin(%pi/20));
                      sqrt(4 - sqrt(2) sqrt(sqrt(5) + 5))
       (%o17)         -----------------------------------
                                      3/2
                                     2

2. ode example

       (%i1) load("trigtools")$
       (%i2) load(odes)$

       (%i3) eq:'diff(y,x,5)+2*y=0;
                                  5
                                 d y
       (%o3)                     --- + 2 y = 0
                                   5
                                 dx

       (%i4) odeL(eq,y,x);
                      1/5     4 %pi
                   - 2    cos(-----) x
                                5              1/5     4 %pi
       (%o4) y = %e                    C5 sin(2    sin(-----) x)
                                                         5
               1/5     4 %pi
            - 2    cos(-----) x
                         5              1/5     4 %pi
        + %e                    C4 cos(2    sin(-----) x)
                                                  5
               1/5     2 %pi
            - 2    cos(-----) x
                         5              1/5     2 %pi
        + %e                    C3 sin(2    sin(-----) x)
                                                  5
               1/5     2 %pi
            - 2    cos(-----) x
                         5              1/5     2 %pi
        + %e                    C2 cos(2    sin(-----) x)
                                                  5
               1/5
            - 2    x
        + %e         C1

       (%i5) sol:trigeval(%);
                     (sqrt(5) - 1) x
                   - ---------------
                           9/5
                          2                 sqrt(sqrt(5) + 5) x
       (%o5) y = %e                  C3 sin(-------------------)
                                                   13/10
                                                  2
              (sqrt(5) - 1) x
            - ---------------
                    9/5
                   2                 sqrt(sqrt(5) + 5) x
        + %e                  C2 cos(-------------------)
                                            13/10
                                           2
            (sqrt(5) + 1) x
            ---------------
                  9/5
                 2                 sqrt(5 - sqrt(5)) x
        + %e                C5 sin(-------------------)
                                          13/10
                                         2
            (sqrt(5) + 1) x
            ---------------
                  9/5                                          1/5
                 2                 sqrt(5 - sqrt(5)) x      - 2    x
        + %e                C4 cos(-------------------) + %e         C1
                                          13/10
                                         2

       (%i6) subst(sol,eq)$
       (%i7) ev(%, nouns)$

       (%i8) radcan(%);
       (%o8)                         0 = 0

3. n-th root of complex number

   Example. Find the 4-th roots of %i

       (%i1) load("trigtools")$

       (%i2) solve(x^4=%i,x);
                       1/8                1/8             1/8
       (%o2) [x = (- 1)    %i, x = - (- 1)   , x = - (- 1)    %i,
                                                                    1/8
                                                           x = (- 1)   ]

       (%i3) rectform(%);
                         %pi        %pi                %pi        %pi
       (%o3) [x = %i cos(---) - sin(---), x = - %i sin(---) - cos(---),
                          8          8                  8          8
                         %pi           %pi              %pi        %pi
                 x = sin(---) - %i cos(---), x = %i sin(---) + cos(---)]
                          8             8                8          8

       (%i4) trigeval(%);
                  sqrt(sqrt(2) + 2) %i   sqrt(2 - sqrt(2))
       (%o4) [x = -------------------- - -----------------,
                           2                     2
             sqrt(2 - sqrt(2)) %i   sqrt(sqrt(2) + 2)
       x = - -------------------- - -----------------,
                      2                     2
           sqrt(2 - sqrt(2))   sqrt(sqrt(2) + 2) %i
       x = ----------------- - --------------------,
                   2                    2
           sqrt(2 - sqrt(2)) %i   sqrt(sqrt(2) + 2)
       x = -------------------- + -----------------]
                    2                     2

Categories: Trigonometric functions · Package trigtools ·

#### 100.2.7 Contract atan Functions ¶

Function: atan_contract (r) ¶

  The function atan_contract(r) contracts atan functions. We assume: \(|r| < {\pi\over 2}.\)

  `load("trigtools")` loads this function.

  Examples:

  1.     (%i1) load("trigtools")$

         (%i2) atan_contract(atan(x)+atan(y));
         (%o2)                   atan(y) + atan(x)

         (%i3) assume(abs(atan(x)+atan(y))<%pi/2)$

         (%i4) atan(x)+atan(y)=atan_contract(atan(x)+atan(y));
                                                   y + x
         (%o4)           atan(y) + atan(x) = atan(-------)
                                                  1 - x y

  2.     (%i1) load("trigtools")$

         (%i2) atan(1/3)+atan(1/5)+atan(1/7)+atan(1/8)$ %=atan_contract(%);
                         1         1         1         1    %pi
         (%o3)      atan(-) + atan(-) + atan(-) + atan(-) = ---
                         3         5         7         8     4

  3. Machin’s formulae

         (%i1) load("trigtools")$

         (%i2) 4*atan(1/5)-atan(1/239)=atan_contract(4*atan(1/5)-atan(1/239));
                                   1          1     %pi
         (%o2)              4 atan(-) - atan(---) = ---
                                   5         239     4

  4. see https://en.wikipedia.org/wiki/Machin-like_formula

         (%i1) load("trigtools")$
         (%i2) 12*atan(1/49)+32*atan(1/57)-5*atan(1/239)+12*atan(1/110443)$

         (%i3) %=atan_contract(%);
                       1             1             1
         (%o3) 12 atan(--) + 32 atan(--) - 5 atan(---)
                       49            57           239
                                                               1       %pi
                                                   + 12 atan(------) = ---
                                                             110443     4

  Categories: Trigonometric functions · Package trigtools ·

### 100.3 References ¶

1. https://maxima.sourceforge.io

#### Footnotes

##### (10)

This is a conversion by hand of the original “trigtools-doc.pdf” file in “share/contrib/trigtools”, by Raymond Toy. See the pdf for the definitive version.

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