Let i = sqrt(-1) which is the conventional notation to set up an imaginary number
The idea is to break up the radicand, aka stuff under the square root, to simplify
sqrt(-8) = sqrt(-1*4*2)
sqrt(-8) = sqrt(-1)*sqrt(4)*sqrt(2)
sqrt(-8) = i*2*sqrt(2)
sqrt(-8) = 2i*sqrt(2)
Answer is choice A
