So we would say c is a critical number of f if and only if, I'll write if with two f's, short for if and only if, f prime of c is equal to 0 or f prime of c is undefined. So if we look for the critical numbers for f, we want to figure out all the places where the derivative of this with respect to x is either equal to 0 or it is undefined. So let's think about how we can find the derivative of this. So let's see, f prime of x is going to be, well let's see, we're going to have to apply some combination of the product rule and the chain rule. So it's going to be the derivative with respect to x of x of x, so it's going to be that, times e to the negative 2x squared plus the derivative with respect to x of e to the negative 2x squared of e to the negative 2x squared times x. So this is just the product rule right over here, derivative of this, of the x, times e to the negative 2x squared plus the derivative of e to the negative 2x squared times x right over here. So what is this going to be?