This is part of the HSC Mathematics Advanced course under the topic of Calculus: Differential Calculus: Differentiation of trigonometric, exponential and logarithmic functions.
In this post, we will explore finding the derivative for sine and cosine. This includes establishing the formulae through numerical estimations of the limits and informal proofs based on geometric constructions.
Eddie Woo: Establishing the Derivatives of \sin x, \cos x and \tan x
Khan Academy: Proof of the derivative of sin(x) (First Principles)
Khan Academy: Derivatives of sin(x) and cos(x) (Visual Understanding)