Abstract: This study arose from the need to provide known elements that allow to more easily reason about the importance and contribution of geometry in the solution of the Pythagorean proposal, assigned to squares of catheti and the square of the hypotenuse in a triangle rectangle. For this, we take a circle inscribed in a quadrilateral whose middle points form a square inscribed in the circle and diagonals of this second square form four isosceles triangles, one of these is taken to demonstrate by construction a particular case (isosceles right triangle) the Pythagorean proposition or theorem.