y² = 7x
It is not a function because, for instance,
(7,7) and (7,-7) are both solutions, since:
(7)² = 7(7)
49 = 49
But also
(-7)² = 7(7)
49 = 49
In a function the same value of x cannot correspond
to two different values of y.
However, (7,7) and (7,-7) have the same x-values
but different y-values.
Also the graph of y² = 7x is this:
And it does not pass the vertical line test, because
these vertical lines (in green) intersect the graph
in two places, which a function cannot have.
Edwin
