The leaning ladder
A ladder leans against a wall: its foot is 3 m out, it reaches 4 m up, and the ladder itself is 5 m long. Those numbers fit 3² + 4² = 5² exactly — the Pythagorean theorem is how builders check a corner is truly square.
a² + b² = c²
In a right triangle, the square of the hypotenuse (the side opposite the right angle) equals the sum of the squares of the other two legs.
Legs 3 and 4: 3² + 4² = 9 + 16 = 25 c = √25 = 5