The problem states: Express Cos( Θ1 + Θ2 + Θ3) in terms of Sin(Θk) and Cos(Θk), k = 1, 2, 3, using the relation e+/-i*Θ = Cos(Θ) +/- i*Sin(Θ). [Hint: Use the product property of the exponential e.g., e(Θ1 + Θ2) = ei*Θ1ei*Θ2.] I'm really confused by in terms of Sin(Θk) and Cos(Θk), k = 1, 2, 3, how does this apply to the problem? I'm really lost, someone please steer me in the right direction. Thanks, Frank Edit: Not sure what's wrong with my &theta ?