So the derivative of that something squared with respect to the something is going to be 2 times that something to the first power. And then we're going to have to make it clear. So this is the derivative of r of t-squared with respect to r of t. The derivative of something squared with respect to that something. If it was the derivative of x squared with respect to x, we'd have 2x. If it was the derivative of r of t squared with respect to r of t, it's 2r of t. But this doesn't get us just the derivative with respect to time. This is just the derivative with respect to r of t. With the derivative, which this changes with respect to time, we have to multiply this times the rate at which r of t changes with respect to time. So the rate at which r of t changes with respect to time, well, we could just write that as dr dt.