Question

use the product to sum formulas to write the product as a sum or difference 10 cos 75° cos 15°

Answer 1

its basically 5cos(75 + 15) + 5 cos(75 - 15)

the terms 5sin75sin15 -5sin75sin15 = 0

will appear

Answer 2

thanks!

Answer 3

but where did you get the 5 from?

Answer 4

its the coefficient of cos(75 + 15)

so 5cos(75 + 15) = 5(cos(75)cos(15) - sin(75)sin(15))
= 5cos(75)(cos(15) - 5sin(75)sin(15)

hope that helps

Answer 5

I got it. haha It came from the two that was divided into the problem