Help with trigonometric equation

Hi all, it's been a while since I took trigonometry in high school and I'm stuck on a current homework problem:

Have to solve for what values of 't' make the equation = 0. 'w' is a constant not equal to 0.

I simplified it because I figured if 'w' is nonzero then only the inside terms mattered:

I've tried setting sin(w*t) to cos(w*t + pi/2) and solving but I ran into problems.. If anyone could give me a hint to point me in the right direction that would be awesome, and maybe if you knew of a good trigonometry refresher kicking around on the internet that would be great as well.