Use the product-to-sum identities and the sum-to-product identities to prove the identity below. cot 4x( sin x + sin 4x + sin 7x) = cos x + cos 4x + cos 7x To verify the identity, start with the left side and transform it to obtain the right side. Choose the correct step and transform the expression according to the step chosen. cot 4x( sin x + sin 4x + sin 7x) = cot 4x (sin 4x + Apply a sum-to-product identity and simplify