Question 379387
A relation is considered a function if every x-value maps to at most one y-value. For example, the equation y = sin(x) is a function, but x^2 + y^2 = 1 is not, since a vertical line at x equals, say, 0, would pass through two of the points. For a relation to be a function, any vertical line drawn must not cross more than one point on the domain/range.