ok so i dont get this question, the integrating factor is clearly sinx from which point i decided that if you minus each side you can abreviate it to $\displaystyle \frac{d(-sinxf)}{dx}=-cos^2xsinx$ NB original question is:$\displaystyle \frac{df}{dx}+fcotx=cos^2x$ the answer is somehow $\displaystyle f(x)=-\frac{cos^3x}{3sinx}+\frac{C}{sinx}$ which i do no understand,,,how can the constand have a sinx underneath is isnt this just another constant? I must be going wrong somewhere on the integral of$\displaystyle \int cos^2dx$ which i make out to be,,,$\displaystyle \frac{co3^3x}{3}$ ? any clues?