Which equation is a quadratic equation?

A.) y + 7 = −3x(4 − x) + 9x
B.) y = −2x + 5
C.) y + 2x^3 = (2x − 2)(x + 5)
D.) y − 9x = (x^2 + 1)(5x − 1) + 3

Question

Which equation is a quadratic equation?

A.) y + 7 = −3x(4 − x) + 9x
B.) y = −2x + 5
C.) y + 2x^3 = (2x − 2)(x + 5)
D.) y − 9x = (x^2 + 1)(5x − 1) + 3

directrix · Answer

Multiply and simplify the options to find one that adheres to the form of the general quadratic as shown on the attached file.

directrix · Answer

Which did you select?

directrix · Answer

B is a line so that is out.
C is a cubic (third degree of x) so that is out.

anonymous · Answer

I am still trying to figure it out but i am leaning more towards letter a maybe

directrix · Answer

I think your answer A is right because looking at this other option: 
y − 9x = (x^2 + 1)(5x − 1) + 3,
there will be an x^3 term when x^2 is multiplied by (5x).

anonymous · Answer

i do agree with you! Thank you for that little picture, it did help me out a bunch!

directrix · Answer

That's good to hear.