This part is going to be defined, and this part is also going to be defined for any value of x. So there's no point where this is undefined, but let's think about when this is going to be equal to 0. So you have this product of these two expressions equaling 0. e to the negative 2x squared, that'll never be equal to 0. If you get this exponent to be a really, I guess you could say very negative number, you will approach 0, but you'll never get it to be, you'll never get it to be 0. So this part here can't be 0, but if the product of two things are 0, at least one of them has to be 0. So the only way that we can get f prime of x to be equal to 0 is when 1 minus 4x squared is equal to 0. So 1 minus 4x squared is equal to 0.