I forgot how this formula $\displaystyle v^2=w^2(a^2-x^2)$ comes in the simple harmonic motion. I mean $\displaystyle v^2=w^2 r^2$ but then how do you substitute $\displaystyle (a^2-x^2)$ in place of r^2. Something to do with circles. Just couldn't find in the M3 book. Please help me or give me some links where i can find this formula.