We have this case right over here. And we'll just do the chain rule, derivative of negative four x with respect to x is negative four. And derivative of e to the negative four x with respect to e, the derivative of e to the negative four x with respect to negative four x is just e to the negative four x. Sometimes you can say this is derivative of the inside times the derivative of the outside with respect to the inside. So either way, it's negative four e to the negative four x for x is greater than zero. So we did the first part, we expressed f prime of x as a piecewise defined function. We didn't define the derivative, actually I forgot a parenthesis here.