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: .
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: .
. . Therefore: .