To find the derivative of cos(θ).

- .

As in the proof of Derivative of Sine, the limit of the first term is and the limit of the second term is 1. Thus

- .

Thus

and so on for ever.

To find the derivative of cos(θ).

- .

As in the proof of Derivative of Sine, the limit of the first term is and the limit of the second term is 1. Thus

- .

Thus

and so on for ever.