We can solve this using Pythagorean Theorem,
c² = a² + b²
where
c = diagonal = hypotenuse = ?
a = leg #1 = 50m
b = leg #2 = 100m
solve for c,
c² = a² + b²
c² = 50² + 100²
c² = 2500 + 10000
c = √12500
c = 111.80 m
So the diagonal is 111.80 meters long.
