Posted by **Kevin** on Sunday, November 13, 2011 at 4:51pm.

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

Answer: sin136+(-62)

2. sin4+sin7 as a product

Answer: 2sin5.5 sin-1.5

3. cos 8x - cos 2x as a product

Answer -2sin5x sin3x

4. cos5x sin9x as a sum

Answer sin14x - (-4)

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

- Trig -
**Steve**, Monday, November 14, 2011 at 10:35am
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.

## Answer this Question

## Related Questions

- trig - I have these sum and product property problems and I just want to make ...
- Math - What is 2 + 2? = 4 What is 2 * 2? = 4 So, the sum and the product of ...
- trig - write equations expressing: 19cos(theta-50degrees) as a sum of sine and ...
- math - Find the two numbers that multiply to the product number and add to the ...
- college math - a pair of dice are rolled and the sum is recorded. What is the ...
- maths - i need help with writing expressions A) double the sum of 25 and 8 i ...
- TRIG! - Posted by hayden on Monday, February 23, 2009 at 4:05pm. sin^6 x + cos^6...
- college math - I do not understand a problem from a text book or how to solve ...
- Physics - Three vectors, each have a magnitude of 30 units, have their tails at ...
- trig - write an equation expressing 19cos(theta-50degrees) as a sum of sine and ...

More Related Questions