Anything to the 0th (if that's a word) power is 1, and a*1=a, so . . .
z18 × z0= x
z18 × 1= x
z18 = x
z18 = z18
(I copied this from a word processor, and it didn't work, so z18 is z to the 18th power, and z0 is z to the 0th power)