If x/y=2 and x*y*a=0, which has to be zero? assuming each variable is a different value. I said a has to be zero but I don't know if this is true or how to write the question.

Answer 1

correct, only a = 0

if x = 0 then in x/y=2
0/y = 2, which cannot be, so x ≠ 0

if y = 0, we would be dividing by zero to get 2, which is rather silly, so y ≠ 0
if a = 0, x/y =2 has nothing to do with it, but
x*y*0 = 0, which is true