Is $y=x^2 + 3x - 15$ a function?

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Answer 1 · 2015-05-21T17:24:25

Yes, it is (in the usual sense that $y$ is a function of $x$ ).

For any value of $x$ , the expression gives only one (never two or more) values for $y$ .

Here is the graph on $y=x^2+3x-15$ . As you can see, it passes the vertical line test.

graph{y=x^2+3x-15 [-33.55, 31.4, -23.03, 9.46]}

(There are many times that 2 values of $x$ give the same value of $y$ , but that is ok for a function.)

Is y=x^2 + 3x - 15y=x^2 + 3x - 15 a function?