You can put this solution on YOUR website! You cannot find the missing side unless you are told it is an isosceles triangle or you are given one of the legs.
You can put this solution on YOUR website! suppose that the triangle is an isosceles right triangle, then we know
s^2 + s^2 = h^2 where s is the length of a side and h is the length of the hypotenuse
2s^2 = h^2
s^2 = h^2 / 2
s = h / sqrt(2)