Square on a (short leg)
9 sq units
Square on b (other leg)
16 sq units
Square on c (hypotenuse)
25 sq units
a² + b² = 9 + 16 = 25 = c²  ✓ they match
Drag the brass dot and the mustard dot to change the two legs. A square sits on every side. Watch it: the two smaller squares ( + ) always add up to the big square on the longest side (). That is Pythagoras' theorem.