Work Step by Step
Assuming that function is expressed as f(x) = y. According vertical line test, each value of x should have unique value of y i.e two different values of x can have same value of y but for single value of x there can not be multiple value of y. For example: f(1) = 2. true f(2) = 2. also true, f(2) = 3. not true, because there is no unique value of y for single value of x = 2. So, a curve crossing the x axis at two different points can be the graph of a function but a curve crossing the y axis at two different points can't.