relation that is not a function

Question

parthkohli · Answer

If one thing points to more than one things, then it's not a function.

mathmale · Answer

This question immediately brings to mind the "vertical line test" that determines from the graph of a relationship whether the relationship is a function or not.  Suppose you had the graph of a circle on paper in front of you and draw a vertical line through that circle.  How many times does the line intersect the circle?  Twice?  Then that graph does NOT represent a function.

anonymous · Answer

equations of circle and ellipse are not functions they are relations

mathmale · Answer

Paraphrasing ParthKohli:  if there is more than one y value for any given x value in a relationship, then the relationship is not a function.

mathmale · Answer

If you were to restrict the range of the circle x^2 + y^2 = 1 to the upper half only, then the resulting graph would represent a function; for any x within the domain of x^2 + y^2 = 1, there would be one and only one y value.