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(1) Express the following product as a sum containing only sine or cosine and no products: sin(40 ) cos (20). [3] (2) Evaluate cos(150) - cos(750). [3] (3) Prove the identity: cos(4t) - cos(2t) = - tant sin (4t) + sin (2t) [3] (4) If f(x) is the function -r+10, if|x| $ 2 f(x) = 2r-, if | |