I'm having trouble getting the answer to this particular question out;

Given that the $\displaystyle \frac{d^2y}{dx^2}$ is equal to $\displaystyle 9\sin3x$;

- Find y if there is a stationary point at $\displaystyle (\frac{\pi}{2}, 1)$
- Show that $\displaystyle \frac{d^2y}{dx^2} + 9y = 0$