500
Is x2 + y2 = 4 a function? Provide evidence for your answer.
No. This relation forms a circle when graphed, which fails the vertical line test. For almost every value of x in the domain, there are two values of y in the range.
or
No. Test points: (0, 2) and (0,-2) both work, so this is not a function because there is more than one y value for this x value.