Simplifying and expressing preferentially with tangents

### 9.2.25 Simplifying and expressing preferentially with tangents

The trigtan command rewrites trigonometric expressions into expressions where as many trigonometric functions as possible are written in terms of tangents, using the identities sin(x)2+cos(x)2=1, tan(x)=sin(x)/cos(x).

- trigtan takes expr, an expression containing trigonometric functions.
- trigtan(expr) returns expr with the trigonometric functions written as much as possible in terms of tangents.

#### Example

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

2 tan4x+3 tan2x+2
tan4x+2 tan2x+1