Question 833040
That is a Special Triangle, with a 90 degree angle and two 45 degree angles.   Each leg equals the other leg.  Call the leg length of one leg x.


{{{x^2+x^2=10^2}}}, because  we have Pythagorean Theorem for sides of a right triangle.
{{{2x^2=100}}}
{{{x^2=50}}}
{{{x=sqrt(2*5*5)}}}
{{{highlight(x=5sqrt(2)) }}}