### 2.21.22 Simplify and express preferentially with tangents : `trigtan`

`trigtan` takes as argument an expression containing trigonometric functions.
`trigtan` 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 tangents.
Input :

`trigtan(sin(x)```^```4+cos(x)```^```2+1)`

Output :

`((tan(x))```^```2/(1+(tan(x))```^```2))```^```2+1/(1+(tan(x)```^```2)+1`

Output, after simplification with `normal` :

`(2*tan(x)```^```4+3*tan(x)```^```2+2)/(tan(x)```^```4+2*tan(x))```^```2+1)`