alleryStart learning →What do the product-to-sum formulas do?
AThey halve the angle inside a trigonometric function
BThey write sums of trigonometric functions as products
CThey write products of trigonometric functions as sums
DThey lower the power of a trigonometric function by one
Answer & Solution
Correct answer: C. They write products of trigonometric functions as sums
1. A product-to-sum formula takes an expression such as cos a cos b and rewrites it without any product of functions.
2. The result is a sum or difference of cosines or sines of the combined angles.
3. So these formulas express products of trigonometric functions as sums.
4. Going the other way, from sums to products, is the job of the sum-to-product formulas.
_Source: OpenStax Algebra and Trigonometry (CC BY 4.0), Ch 9 "Trigonometric Identities and Equations", section 9.4 Sum-to-Product and Product-to-Sum Formulas_
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