### 2.21.6 Transform arccos into arcsin : `acos2asin`

`acos2asin` takes as argument an expression containing
inverse trigonometric functions.

`acos2asin` replaces arccos(*x*) by
π/2−arcsin(*x*), in this expression.

Input :

`acos2asin(acos(x)+asin(x))`

Output after simplification :

`pi/2`