Writing \cos(\theta)=\sin(\theta-\pi/2), use the derivative of the sine function together with our shifting slope problem to explain why

\frac{d}{dx}\cos(x) = -\sin(x).

Writing \cos(\theta)=\sin(\theta-\pi/2), use the derivative of the sine function together with our shifting slope problem to explain why

\frac{d}{dx}\cos(x) = -\sin(x).