cos²Θ = cos²Θ – sin ²Θ

Are you sure this is the right identity?

I'm pretty sure you meant

cos2\theta = cos^2\theta - sin^2 \theta

then, on the left hand side;

cos2\theta = cos(\theta + \theta)

cos(\theta + \theta) = cos\theta cos\theta - sin\theta sin\theta

cos\theta cos\theta - sin\theta sin\theta = cos^2\theta - sin^2 \theta

Note, you make use of the identity

cos(A + B) = cosA cosB - sinA sinB

Prove (Sin5A - Sin4A)/(Cos4A + Cos5A) = Tan A/2

DESPERATE NEED OF HELP!

Prove (Sin5A - Sin4A)/(Cos4A + Cos5A) = Tan A/2

DESPERATE NEED OF HELP!!

Start your own thread instead of using an old one. You are more apt to get help that way.