Question

Can somebody explain to me why cos2x = cos2x - sin2x?

Answer 1

You mean Cos(2x) = Cos^2(x) - Sin^2(x)

Answer 2

Look up the formula for Cos(A+B) and post it here.

Answer 3

Oh, ok. cos(A+B) = cos(A)cos(B) - sin(A)sin(B)

Answer 4

Oh, yeah. Sorry. It is squared. Cos(2x) = Cos^2(x) - Sin^2(x)

Answer 5

Okay, so in your case you have:
Cos(2x) = Cos(x+x) = Cos(x)Cos(x) - Sin(x)Sin(x) = ...

Answer 6

Do you get it?

Answer 7

Ah. I see. Thanks.

Answer 8

Np