i suppose you mean distinct numbers y and y', of course.2) If x is any number, there do not exist two numbers y and y' such that x*y = 1 and x*y' = 1.
assume to the contrary that there does exist distinct numbers y and y' such that
x*y = 1.........(a) and,
x*y' = 1 ........(b)
subtracting (b) from (a) we get
x*y - x*y' = 0
=> x(y - y') = 0
thus, x = 0 or y = y'
in either case, we have a contradiction. (do you see why? in particular, why does x = 0 yield a contradiction?)