Learn how to solve problems step by step online. Prove the trigonometric identity cos(f+pi/2)=-sin(f). Starting from the left-hand side (LHS) of the identity. Using the cosine of a sum formula: \cos(\alpha\pm\beta)=\cos(\alpha)\cos(\beta)\mp\sin(\alpha)\sin(\beta), where angle \alpha equals f, and angle \beta equals \frac{\pi }{2}. The sine of \frac{\pi }{2} equals 1. Multiply -1 times 1.

Prove the trigonometric identity cos(f+pi/2)=-sin(f)