Answer:
E 10 sqrt(2)
Explanation:
If this is an isosceles triangle than AB = BC and AB = 10 so BC = 10
We want to us the Pythagorean theorem since it is a right triangle
a^2 + b^2 = c^2 where a and b are the legs and c is the hypotenuse
10^2 + 10^2 = AC^2
100 + 100 = AC^2
200 = AC ^2
Take the square root of each side
sqrt(200) = sqrt( AC^2)
sqrt(100*2) = AC
We know sqrt(ab) = sqrt(a) sqrt(b)
sqrt(100) sqrt(2) = AC
10 sqrt(2) = AC