# Trig

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I have these sum and product property problems and I just want to make sure my work is right.

Write equations expressing
1. cos 37degrees cos99degrees as a sum
2. sin4+sin7 as a product
3. cos 8x - cos 2x as a product
4. cos5x sin9x as a sum

Idk...I just don't feel as confident about these

• Trig -

recall that

cosa * cosb = 1/2[cos(a+b) + cos(a-b)]

cos37 cos99 = 1/2(cos126 + cos(-62))
= 1/2 (cos126 + cos62)
since cos(-a) = cos(a)

So, your answers have the right number sin them, but you need to tidy them up to conform to the identities.

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