Simplifying and expressing preferentially with cosines

### 9.2.24 Simplifying and expressing preferentially with cosines

Any trigonometric function can be written in terms of sins and coss, and with the identity sin(x)2+cos(x)2=1, the even powers of sin can be turned into powers of cos. The trigcos command performs these substitutions.

- trigcos takes expr, an expression containing trigonometric functions.
- trigsin(expr) returns expr with the trigonometric functions rewritten in terms of sin and cos, with as many sins as possible transformed to coss.

#### Example

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

cos4x−cos2x+2 |  |  |  |  |  |  |  |  |  |