Question

I don't understand the point of cofunction identities, like I know how to solve problems with it but I don't know how to make sense of it. Can someone please explain it?

Answer 1

\[f(\frac{\pi}{2}-\theta)=cof(\theta)\]

Answer 2

for example
\[\sin(\frac{\pi}{2}-\theta)=\cos(\theta)\] and so on