### Proof > let x be the sum ### LaTeX ``` c = x - (a + b) \\ a^2 + b^2 = (x - (a + b))^2 \\ a^2 + b^2 = a^2 + 2ab - 2ax + b^2 - 2bx + x^2 \\ 2ab - 2ax - 2bx + x^2 = 0 \\ \\ 2bx - 2ab = x^2 - 2ax \\ (\frac{x^2}{x}) - 2a = 2b - (\frac{2ab}{x}) \\ -2a = 2b - (\frac{2ab}{x}) - (\frac{x^2}{x}) \\ \\ a = \frac{2bx - x^2}{2x - 2b} ```