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. Let me rewrite that. 1 minus 4x squared is equal to 0. When does that happen?