We didn't define the derivative, actually I forgot a parenthesis here. We didn't define the derivative when x is equal to zero because it's actually not going to be defined there. Now let's do the second part. Find the value of x for which f prime of x is equal to negative three. And so if this wasn't piecewise defined, you'd just very simply just say, oh look, f prime of x is equal to negative three. You would take whatever f prime of x is equal to and you'd do some algebra to solve for it. But here you're like, well which case do I use?