Question

2cos(3x)

Answer 1

Hello, and welcome to Open Study!

Please, would you include the instructions that came with this problem?

Suggestions: Hold that "2." Determine a way to write cos 3x in terms of cos x and sin x only.

Hint: Use the sum formula for the cosine function: cos (x+y) = cos x cos y - sin x sin y.

Answer 2

Are you allowed to use a calculator?

Answer 3

Thank, I found the answer already. Sorry for the incomplete of the question.
Actually it is a part of answer from a differentiation, then I need to use trigonometry to solve it. I just want to know the 2cos(3x)= ?? to continue my calculation.
Whatever, thank you all.