Any isosceles triangle has 2 legs with the same length.
L=length of the leg in this isosceles triangle.
Applying the Pythagorean theorem :
(leg a)² + (leg b)²=hypotenuse²
In this case (isosceles triangle):
L² + L²=(50 m)²
2L²=2500 m²
L²=2500/2 m²
L²=1250 m²
L=+√(1250 m²)≈35.36 m
Answer: the measure of each leg will be 35.36 m.