1. The problem statement, all variables and given/known data Equation of a wave is a = a°sin(ωt - kx + φ) where φ is the phase of a wave. if 2 waves with phases φ1 and φ2 interfere, show how the intensity I =a² varies as a function of the phase difference φ1 - φ2. Use one of the trigonometric double angle forumula or otherwise to obtain your result. 2. Relevant equations The double angle formulas 3. The attempt at a solution Well am I supposed to map I =a² onto the equation? If so then the only double angle formula is cos(2x) = cos²(x) - sin²(x) But I get a really stupid answer when I square the wave equation.. What do I do?