Pythagoras theorem In Figure 2(a), a right triangle with legs and is moved a distance in the direction perpendicular to its hypotenuse . The area swept by the triangle is then a rectangle with area . On the other hand, the same area is swept by the triangle if we slide it horizontally a distance and then slide it vertically a distance , i.e. (adding and subtracting a small right-angled triangle). Now we use the sliding argument twice (one for the horizontal translation and the other one for the vertical translation of the triangle) to give and , so . Noticing the similarity between two right triangles, when we have and , and we get the Pythagoras formula . See also Figure 3, where the areas with the same colour are seen to be equal by the sliding argument (or, if one wishes, because they correspond to parallelograms which are on the same base and between the same parallels).