In the movie Wizard of Oz what is the name of the theorem that the scarecrow stated when he got a brain?

The Scarecrow states an incorrect version of the Pythagorean theorem.

He states: "The sum of the square root of two sides of an isosceles triangle is equal to the square root of the third side."

There are two errors. The Pythagorean theorem applies to right triangles, not isosceles. Also the theorem is that the squares of two legs equals the square of the hypotenuse.

Properly stated, "The sum of the squares of the two legs of a right triangle is equal to the square of the hypotenuse."

He said...

"The sum of the square roots of any two sides of an Isosceles triangle is equal to the square root of the remaining side. Oh joy, rapture, I've got a brain. How can I ever thank you enough?"