Question

Which expression is equivalent to square root of -108 minus square root of -3

Answer 1

5 sqrt 3i is the correct answer

Answer 2

Sqrt(-108) - sqrt(-3) produces two imaginary terms:  -i*sqrt( 36*3) -i*sqrt( 3).
Let's simplify that:

-i [ 6*sqrt(3) - 1*sqrt(3) ]     =     -i * 5* sqrt( 3)    (answer)