Answer: C
Explanation:
the rule for a 45 45 90 triangle is
the legs are proportionally x
and the hypotenuse is x√2
AB is a leg, which is x =5
BC is hypotenuse = x√2 = 5√2
or if you don't remember rules use pythagorean
c²=a²+b² in this problem a and b are the same since the 2 angles are the same
c²=5²+5²
c²=25+25
c²=50
c=√50
=
square root of 25 is 5 so that can come out of root, 2 stays in
=5√2