text: Equation
  
  • Mar 11th 2011, 11:19 AM
  Critter314
  Equation
  How to prove?
  $cos 2x + cos x = sin^2 x$
  All Ive got so far is $cos^2 x - sin^2 x + cos x = sin^2 x$
  • Mar 11th 2011, 11:23 AM
  emakarov
  Let's see, cos(2 * 0) + cos(0) = 2. Hmm...
  • Mar 11th 2011, 11:36 AM
  TheChaz
  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.