### 5.21.21 Simplify and express preferentially with sine : trigsin

trigsin takes as argument an expression
containing trigonometric functions.

trigsin simplify 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 sine.

Input :

trigsin(sin(x)`^`

4+cos(x)`^`

2+1)

Output :

sin(x)`^`

4-sin(x)`^`

2+2