Hello, decoy808!

This is how I would do it . . .i already have done part (i) . . . . but you didn't finish

(i) Express: . in the format:

We have: .

Multiply by

Let be in a right triangle with: .

. . Then: .

Then we have: .

From a Compound-Angle Identity: .

Since , then: .

(ii) Using your answer to part (i), solve: .

So we have: .

. . which becomes: .

Then: .

. . Therefore: .