Mathematics
Galois Theory: Solving Polynomials by Radicals
Quick fact
While quadratic, cubic, and quartic equations all have general radical formulas, there is no such formula for general polynomials of degree 5 or higher—a result proven by Galois and Abel.
Why this is interesting
You've used the quadratic formula, but what if there were no formula for higher-degree equations? Some polynomials simply cannot be solved by radicals—and Galois theory explains why.