qqp question1: Why is the derivative of [math]uv[/math] equal to [math]uv' + vu'[/math] ? question2: How do I understand intuitively this formula [math]\frac{d(f(x)g(x))}{dx} = f(x)\frac{dg(x)}{dx}+\frac{df(x)}{dx}g(x)[/math]?