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Prove the following identities. 1. cos(A + B) = cos A cos B - sin A sin B 2. sin 20 = 2 sin 0 cos e Solve the following trigonometric equation. 3. Given f(x) = 3 sin(1.5x - 0.8) + 7, solve f(x) = 8.5 Keep in mind the solution set is infinite. Express your answers in the form x = a + bn where a, b E R and n E Z. For example: x = 0.17 + 2.4n