Geometry math question no Guessing and Please show work

because the 2 sides are the same, we know this is a 45-45-90 triangle. A 45-45-90 triangle as side lengths of x-x-x√2
because the sides are the same, we know they are the x, so x√2 is the final number
√10*√2 = √20 = √4*5 = B. 2√5