(x + 5)^2 + (x - 10)^2 = 2x^2;

x^2 + 10x + 25 + x^2 - 20x + 100 = 2x^2;

x^2 + x^2 - 2x^2 + 10x - 20x = -100 - 25;

x(10 - 20) = -125;

-10x = -125;

x = -125 : (-10);

x = 12.5.