1. Shear the squares on the legs by dragging point P, then point Q, to the line. Shearing does not affect a polygon''s area.
2. Shear the square on the hypotenuse by dragging point R to fill the right angle.
3. The resulting shapes are congruent. The sum of the squares of the sides equals the square on the hypotenuse.
[Based on Euclid's Proof]