Answer:
See Below.
Explanation:
We are given that:

Part 5.2.1
Note that:

Then from the given identity:

Cosine is an even function and sine is an odd function. That is:

Hence:

Part 5.2.2
We want to verify that:

From the identity:

Since A + B = 90°, A = 90° - B. Hence:

Sine and cosine are co-functions. That is:

Hence:

And by squaring both sides:
