Question 661000
If the legs are x and 2x, by the Pythagorean theorem:

x^2 + (2x)^2 = c^2 where c is the length of the hypotenuse.

{{{x^2+4x^2=c^2}}}
{{{5x^2 = c^2}}}
{{{sqrt(5x^2) = sqrt(c^2)}}}
{{{sqrt(5)*x = c}}}