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## Main Question or Discussion Point

The question states, "Prove the identity."

(1) cos(x + y) cos(x-y) = cos(^2)x – sin(^2)y.

Should i start off using the addition and subtraction formulas for the LHS, and breaking down the perfect square for the RHS? If not or if so, how would I go about solving this problem? Step by step.

(2) sin(x + y + z) = sinx cosy cosz + cosx siny cosz + cosx cosy sinz - sinx siny sinz.

I started this off using the addition formula for the LHS, but I ended up splitting the LHS into two separate identities: sin(x + y) sin(y + z). How do I approach this problem?

(1) cos(x + y) cos(x-y) = cos(^2)x – sin(^2)y.

Should i start off using the addition and subtraction formulas for the LHS, and breaking down the perfect square for the RHS? If not or if so, how would I go about solving this problem? Step by step.

(2) sin(x + y + z) = sinx cosy cosz + cosx siny cosz + cosx cosy sinz - sinx siny sinz.

I started this off using the addition formula for the LHS, but I ended up splitting the LHS into two separate identities: sin(x + y) sin(y + z). How do I approach this problem?