Consider a triangle, with one angle right. Construct three more just like it, all equal by sight. Arrange them into a square, long sides in middle, shorter sides on the outside, long next to little. 

As area of the whole is sum of the parts, so the triangle and square which long sides demark are equal in area to the square outside. Thus yielding the conclusion which can't be denied that the hypot'nuse's length, upon being squared, equals the sum of squared lengths of the shorter pair. 

ca. 1990 