### 2.21.4 Put together sine and cosine of the same angle : `tcollect tCollect`

`tcollect` or `tCollect` takes as argument an expression containing trigonometric functions.
`tcollect` first linearizes this expression (e.g. in terms of sin(n.x) and cos(n.x)), then, puts together sine and cosine of the same angle.
Input :

`tcollect(sin(x)+cos(x))`

Output :

`sqrt(2)*cos(x-pi/4)`

Input :

`tcollect(2*sin(x)*cos(x)+cos(2*x))`

Output :

`sqrt(2)*cos(2*x-pi/4)`