Question 987948
Either leg, x.
Such a triangle is half of a square, and each leg serves as base or height.
{{{cross((1/2)x^2=200/2)}}}-------off-target.....
{{{(1/2)x^2=200}}}, the the area of the isosceles right triangle.


<s>What is 4x ?</s>


You also want to know the length of the hypotenuse, which would be the diagonal of the square from which this triangle comes.


{{{x^2=400}}}
{{{x=20}}}


NOW, if h is the hypotenuse,
{{{x^2+x^2=h^2}}}
{{{h^2=2x^2}}}
{{{h=x*sqrt(2)}}}
{{{h=20*sqrt(2)}}}


You have now the data needed to find the perimeter of the triangle.