# Thread: [SOLVED] Trig Equivalency question?

1. ## [SOLVED] Trig Equivalency question?

we know that $cos^2(x) = 1/2(1+cos(2x))$

could I say that $cos^2(3x)=1/2(1+cos(6x))$ ?

2. Originally Posted by doomgaze
we know that $cos^2(x) = 1/2(1+cos(2x))$

could I say that $cos^2(3x)=1/2(1+cos(6x))$ ?
Difinetly you can say so.

3. Originally Posted by sa-ri-ga-ma
Difinetly you can say so.
I guess more importantly is it correct?

4. Yes.

--Kevin C.

5. Originally Posted by doomgaze
I guess more importantly is it correct?
If 3x= t
6x= 2t.
cos(2t) = 2cos^2(t) - 1
so 2cos^2(t) = 1+cos(2t)

cos^2(t) = 1/2(1+cos(2t))

replace t by 3x and find the result.