I could say u is equal to x squared plus one, in which case the derivative of u with respect to x is just two x plus zero, or just two x. I could write that in differential form. A mathematical hand-wavy way of thinking about it is multiplying both sides by dx. And so you get du is equal to two x dx. And so at least this part of the integral I can rewrite. So let me at least write, so this is going to be, I'll write the integral. We're gonna think about the bounds in a second. So we have u to the third power.