We're taking the log base four, not just of x, but we're taking that of another expression that involves x. So we could say, we could say this thing in blue, that's u of x. Let me do that in blue. So this thing in blue, that is u of x. U of x is equal to x squared plus x. And it's going to be useful later on to know what u prime of x is. So that's going to be, just going to use the power rule here. So two x plus one, brought that two out front and decremented the exponent.