Use the product-to-sum identities and the sum-to-product identities to prove the identity below. sin 40+ sin 60=cot 0(cos 40- cos 60) 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. sin 40+ sin 60 = Apply a sum-to-product identity and simplify.