Which equation is a quadratic equation?

3x − y = 8x + 2

y = 7x(5 − 2x) + 9

7x2 + y = (3 + x)(7x − 1)

y − 3 = (x2 − 3)(8x + 3)

Question

Which equation is a quadratic equation?

 3x − y = 8x + 2

 y = 7x(5 − 2x) + 9

 7x2 + y = (3 + x)(7x − 1)

 y − 3 = (x2 − 3)(8x + 3)

mertsj · Answer

You are looking for the answer which has 2 for its largest exponent.

agent0smith · Answer

Simplify them first as much as possible, by expanding/distributing, combining like terms etc.

anonymous · Answer

@Mertsj How would I do that?

anonymous · Answer

Oh is it C?

agent0smith · Answer

Like I said, simplify them first, by expanding it all out, FOILing etc

mertsj · Answer

In the first one it is obvious that the largest exponent is 1

agent0smith · Answer

Because if you can't tell by eyeballing them, you'll need to simplify. C may look quadratic, but what happens if you expand it out and simplify?

mertsj · Answer

What do you get when you multiply the second one and collect like terms?

anonymous · Answer

y = 35x - 14x^2 + 9

agent0smith · Answer

^ which has an x^2 term as it's highest power, making it a quadratic.

mertsj · Answer

So I see the largest exponent is 2 and there is your answer.

anonymous · Answer

Thank you both so much as always!!