But I'm used to seeing the x or the function x as the upper bound, not as the lower bound. How do I deal with this? And the key realization is to realize what happens when you switch bounds for a definite integral. And I'll do a little bit of an aside to review that. So if I'm taking the definite integral from a to b of f of t dt, we know that this is capital F, the antiderivative of F evaluated at b, minus the antiderivative of F evaluated at a. This is essentially corollary to the fundamental theorem, or it's the fundamental theorem part two, the second fundamental theorem of calculus. This is how we evaluate definite integrals.