Hello, aeroflix!
The answers are truly ugly . . . but they check out!
I'll baby-talk through this for you . . .
.[1]
Let
. . Then: .
So is in a right triangle with: .
. .
Hence: .
Then [1] becomes: . .[2]
We need this identity: .
Take the tangent of both sides of [2]:
. .
. .
So we have: .
. . which simplifies to: .