The area of each triangle is ½ × ( A × B )

The area of the inner square is ( A - B )^{2}

The area of the outer square is:

C^{2} = 4 × ½ × ( A × B ) + (A - B)^{2}

C^{2} = 2AB + A^{2} - 2AB + B^{2}

C^{2} = A^{2} + B^{2}