Showing that it's not a function

How do I show that (x+1)^2 + (y-1)^2 = 4 is not a function by giving a value of x to which there corresponds more than one y?

you need one example ,
where for one x
you have two different y

take x=-1
then
(y-1)^2 = 4

y-1 = (+/-)2
y=3
or
y=-1

(-1,3) (-1,-1)
on a vertical line x=-1

two intersections with graph
so this is not afunction

(x+1)^2 + (y-1)^2 = 4
(y-1)^2 = 4 - (x+1)^2
(y-1)^2 = 4 -x^2 -2x -1
(y-1)^2 = -x^2 -2x + 3
(y-1) = sqrt(-x^2 -2x + 3)
y = 1 +/- sqrt(-x^2 -2x + 3)

since it's plus or minus, there are 2 y's for an x
let x = -2
y = 1 +/- sqrt(-4 + 4 + 3)
y = 1 + sqrt(3) ; 1 = sqrt(3)

You have to solve for y using algebra, to show a positive or negative x.