The large squares above both have equal areas since both are of sideTo produce the large square on the right arrange the red and blue triangles from the square above left around the outside as shown.The area of the large square above left is given byThe area of the large square above right is given byor Equating these two givesExpanding and simplifying givesand cancellingfrom both sides gives- this is Pythagoras theoremNote thatare the sides of one of the red or blue right angled triangles, with being the longest side.