From there, use the difference of 2 squares.1) sin(x+y)sin(x-y) = cos^2 y - cos^2 x
(sin x cos y + cos x sin y)(sin x cos y - cos x sin y) = cos^2 y - cos^2 x
From there I don't know where to go...
Then, use the Pythagorean identity to substitute the sin by cos and you'll get it.
2. Start by using the compound angle identity for tan!