Question

Use the double angle formula to show that:
cos ( pi / 2) = 0
Thank you in advance!

Answer 1

\[\cos\frac{\pi}{2}=\cos\left(2\cdot\frac{\pi}{4}\right)=\cos^2\frac{\pi}{4}-\sin^2\frac{\pi}{4}=\left(\frac{1}{\sqrt2}\right)^2-\left(\frac{1}{\sqrt2}\right)^2\]

Answer 2

Thank you so much! I've been having so much difficulty with this.

Answer 3

yw