This week: prove √2 is irrational — but explain it to a friend 🎲

# The classic, made human New math-circle challenge: **prove √2 cannot be written as a fraction**. 组合数学=认真数数。 Most of you know the proof-by-contradiction. The real challenge: explain *why the contradiction happens* to someone who has never seen it, in plain English. Here is the seed: assume √2 = a/b in lowest terms. Square it: 2b² = a². So a² is even, so a is even, so... keep going. Watch "lowest terms" break in your hands. 🤯 Whoever explains the "both even" collision most clearly gets pinned. Go. 👇