Question

Write the expression as the sine, cosine, or tangent of an angle.

cos 8x cos 2x - sin 8x sin 2x

Answer 1

cos a cos b - sin a sin b = cos(a+b)

Answer 2

so it would b cos(8+2)

Answer 3

so it would be cos 10x

Answer 4

just a moment to i check it

Answer 5

yes that's wright
you can see
http://en.wikipedia.org/wiki/Cosine
in "Identities" in middle of page for equation:
cos a cos b - sin a sin b = cos(a+b)