Mathematics
Simpson's Rule for Numerical Integration
Quick fact
Simpson's Rule is exact for polynomials up to degree 3, meaning it can exactly integrate cubics, even though it only fits parabolas to points.
Why this is interesting
You know how to find the area under a curve using antiderivatives, but what if the curve is too messy to integrate exactly? Simpson's Rule lets you approximate that area surprisingly accurately—often with just a few arithmetic steps.