# Equation

• March 11th 2011, 11:19 AM
Critter314
Equation
How to prove?
$cos 2x + cos x = sin^2 x$
All Ive got so far is $cos^2 x - sin^2 x + cos x = sin^2 x$
• March 11th 2011, 11:23 AM
emakarov
Let's see, cos(2 * 0) + cos(0) = 2. Hmm...
• March 11th 2011, 11:36 AM
TheChaz
It should read "solve", and we've already addressed this (7 minutes ago) at mymathforum!

I'm ok with you replying in either place... Obviously ;)
• March 11th 2011, 07:40 PM
Prove It
Now substitute $\displaystyle \sin^2{x} = 1 - \cos^2{x}$ to get a quadratic equation in $\displaystyle \cos{x}$, which you will be able to solve.
• March 12th 2011, 04:54 PM
TheChaz
Yeah, I said that already! ;)