what is the origin of the pythagorian theorem?

We'll start from the fact that if we'll construct a square
whose one side lies on the hypotenuse of a right angle triangle, we'll notice that the
area of this square is equal to the sum of areas of the squares whose one side lies on
each leg of this triangle.

If we'll note the length of
hypotenuse as`` z, the area of the square is `z^(2)`.

If
the lengths of the legs are x and y, therefore the areas of the squares are `x^(2)` and
`y^(2)` .

Therefore, according to Pyhtagorean theorem,
we'll  get:

`x^(2)` + `y^(2)` =
`z^(2)`