Quick questions on Product-to-sum and sum-to-product identities for trigonometric expressions

2short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What are the four product-to-sum identities?

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These come from adding or subtracting the sum and difference identities:

What is inconsistent units inside the identity?

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A + B

and

A - B

must be evaluated in radians or degrees consistently. Mix the two and the answer is wrong.

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