Question 8083
Yes, it is the pythagorean formula.

You are trying to find point (x, 0) where the y coordinate is zero, since it is on the X axis. 

Points (1, 3), (1, 0), and (x, 0) form a right triangle. One side of it has length one. Another has length x-1. Sum of their squares should be 5:

{{{1^2+(x-1)^2) = 5}}}

*[invoke explain_simplification "1^2+(x-1)(x-1)=5"]