ddx[f(x)g(x)]=f′(x)g(x)+f(x)g′(x) \frac{d}{dx}\left[f(x)g(x)\right] = f'(x)g(x) + f(x)g'(x) dxd[f(x)g(x)]=f′(x)g(x)+f(x)g′(x)