how did you calculate the cos(3x) how is that broken down?
i know cos(2x) is cos(x)cos(x) - sin(x)sin(x)
but how did u do this one
Yes, and
Write and use the sum formula: cos(a+ b)= cos(a)cos(b)- sin(a)sin(b) so that cos(3x)= cos(2x)cos(x)- sin(2x)sin(x). Now put the formulas form cos(2x) and sin(2x) into that.