recall cos(A + B) = cosAcosB - sinAsinB
you just have an application of this.
then ...
cos 2x = cos(x+x)
= cosxcosx - sinxsinx
= ....
simple question
how come
cos^2(x)-sin^2(x) = cos(2x)
where the identity cos(2x) come from?
thanks a lot
1 answer
1 answer