Question

Write as a single trig function: cos²3M-sin²3M

Answer 1

i have no idea why this equals
cos(3M)

Answer 2

is there any identity related to this?

Answer 3

cos^2(3M) = 1-sin^2(3M). So, you can substitute and write it in terms of sin.

Answer 4

wouldn't that equal 1 then?
cos²3M-sin²3M
= 1-sin²3M-sin²3M
= 1?

Answer 5

No, it will be 1-2*sin^2(3M).

Answer 6

oh my mistake. thank you!