Question 979163
This is NOT a function because it's possible to have x values correspond to more than one y value. It fails the vertical line test. This figure is an ellipse.


If x = 1, then y = +-2. The fact that x = 1 corresponds to y = 2 and y = -2 means we don't have a function. The x value of 1 must correspond to EXACTLY ONE y value only.