if we assume this is a right triangle
for a right triangle
if it has legs length a and b and hyptonouse c then
a²+b²=c²
given
a leg is 24
hyptonuse =25
the other leg is b
24²+b²=25²
576+b²=625
minus 576 from both sides
b²=49
sqrt both sides
b=7
the other leg is 7 units
