### 5.21.22 Simplify and express preferentially with cosine : trigcos

trigcos takes as argument an expression
containing trigonometric functions.

trigcos simplifies this expression with the formula :

sin(x)^{2}+cos(x)^{2}=1, tan(x)=sin(x)/cos(x) and
tries to rewrite the expression only with cosine.

Input :

trigcos(sin(x)`^`

4+cos(x)`^`

2+1)

Output :

cos(x)`^`

4-cos(x)`^`

2+2