Hello, Keither!

Instead of wrestling with various identities,

. . why not use the method I've used . . . "build the triangle."

Find

Since , we have: .

From , we have: .

In , opposite is positive:

We know all three sides of the triangle: .

We can writeanyfunction now: .

This time using identities is faster . . .

We have: .

. . Then: . . . . (positive in Q1)

We have: .

. . Then: . . . . (positive in Q1)

Therefore: .