Conceptual nature of reversing the limits of an integral Let's say I integrate $$\int_5^0 x^2 \, dx$$
i.e.$-\frac{125}{3}$, what is physically happening with the summing of strips to produce a negative answer?
Cheers
Tom

In terms of the literal definition of the (Riemann) integral, you always have ending points of small subintervals for integration that are BEFORE (less than) the starting points, so when you take the differences between subinterval endpoints ("deltas") in the definition of a Riemann integral, you wind up with a minus sign in front of the integral you would get if you swapped the limits of integration.
