This puzzle is based on a proof of the Pythagorean theorem, which states that for any right triangle with a hypotenuse of length A other two sides of lengths B and C then
A*A = B*B + C*C.
The idea of the proof is to calculate the area of the large square in two ways; as the product of its sides and as the sum of the areas of the pieces.
In this puzzle we have a square that has been divided into 4 congruent right triangles and a smaller square. If we call the lengths of the triangle sides A, B and C, such that
• A is the length of the hypotenuse
• B is the length of the longer remaining side
• C is the length of the shorter remaining side
then the area of each right triangle is B*C/2 and the area of the inner square is (B - C)*(B - C). Thus the area calculated in these two ways must be the same so we have the following equation: