If sin(2x) =0 tanx - cos 2x, then sinx - cosx =?

I know of all the double angle identies for sin and cosine, and I know tan=sin/cos.

I still can't manage to find sinx-cosx

Perhaps you can get me in the right direction.. I tried subbing a few identites, but apparently not the right ones. And note that this problem isn't for class.... This is from Princeton Review math lvl 2 review.