Question

Prove that CosB-cosA/cosA+cosB=tanA+B/2tanA-B/2

Answer 1

use your sum-to-product formulas:

cosB-cosA = 2 sin (A+B)/2 sin (A-B)/2
cosA+cosB = 2 cos (A+B)/2 cos (A-B)/2

now just divide

Answer 2

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