Find the derivative of `cos(2x+1)` w.r.t. x from first principle.

Explanation

Here, `f(x) = cos(2x+1)`

`:. f'(x) = Lim_(h->0) (f(x+h) - f(x))/h`

`= Lim_(h->0) (cos(2(x+h)+1) - cos(2x+1))/h`


`= Lim_(h->0) (-2sin(4x+2h+2)/2sin((2h)/2)/h`

`= -2 Lim_(h->0) (sin(4x+2h+2)/2sin(h))/(h)`

`= -2 Lim_(h->0) sin(4x+2h+2)/2 *Lim_(h->0) sin(h)/(h)`

`=-2sin(2x+1)*1`

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