Cos 3x

If you keep going, you'll see the cosines of all the multiples of x have only even powers of sin x, so you can . Name: Joshua Who is asking: Student Level of the question: All. Question: I'm having trouble proving that cos(3X)=cos cubed X -(cosX)(sin squared X) .

I know cos ⁡ x = cos ⁡ ( x + x ). So know I have cos ⁡ x + cos ⁡ x , Which is ( cos ⁡ x − ) cos ⁡ x. But I am not sure what to do next. X) = 3sinX - 4sin 3X cos(3X) = 4cos 3X - 3cosX sin(4X) = 4sinXcosX - 8sin 3XcosX cos(4X) = 8cos 4X - 8cos 2X + 1 . A+B), cos(A+B), double angle formulae, and identity relationship between sinx and cosx. Using basic identities to simplify the expression. How to simplify cosx-cos^3x I know the answer is cos(x)sin^2(x) But I just don't know how to .