differentiation of cosx by first principle

In this video "Derivative or differentiation or differentiating of Cos(x)=-Sin(x) from First Principles Proof" we will prove that the derivative of cos(x) is -sin(x) by using first principles. You will also get some practice of taking limits.

In our Previous we also have learnt how we can prove sinx=cosx and Tanx= Sec^2x by first principle