## Pythagorean Theorem. Out of the blue?

When I first heard the Pythagorean Formula, I wondered where did Pythagoras get the idea of that relationship? The teacher showed a right triangle and drew squares upon each side.

That was so unintuitive to me. It was a deduction after the fact. Although the drawing was explicit (Figure 1), it didnâ€™t motivate my understanding of why the formula was valid or suggest a method for proving it.

Years later, I stumbled across a construction that makes much more sense. Consider a square (Figure 2). Divide a side anywhere into two parts, named a and b. Then from the first a draw a straight line to point a on the adjacent side. Do the same to the third side, the fourth side, then close the **inscribed square** by drawing a straight line from the fourth side to the original point a.

Figure 2 shows the original square of side a+b and the inscribed square of side c.Â

Area of original square = Area of inscribed square + 4* identical right triangles

(a + b)^{2} = c^{2 }+ 4(Â½ ab)

a^{2 }+ 2ab + b^{2} = c^{2 }+ 2 ab

**a ^{2} + b^{2} = c^{2}**

Perhaps some other teachers developed the inscribed square to explain the Pythagorean Theorem. I wish mine had.

Image Pythagorean Triangle with squares on each side. en:User:Wapcaplet, CC BY-SA 3.0 http://creativecommons.org/licenses/by-sa/3.0/, via Wikimedia Commons