$\int\ cos^3xsin2x$
i first split up $cos^3x$ into $cosx(1-sin^2(x))$ and i said $sin2x= 2sinxcosx$. this is apparently the correct approach, but when i did it on my quiz today, i ended up getting $-1/10 cos^5x +c$instead of $-2/5 cos^5x +c$. the latter is the correct answer.. can someone help me find my mistake?