Question 705226
Use Pythagorean Theorem.

If you divide the square diagonally, the diagonal will become the hypotenuse of the triangle whose sides(x) are equal since it is a square.

So the formula is:
{{{x^2+x^2=125^2}}} 
{{{2x^2=125^2}}}

Solving for x, we get:
{{{x=125/sqrt(2)}}} or 88.39