Which function is a quadratic function?
u(x) = –x + 3x2 – 8
v(x) = 2x2 + 8x3 + 9x
y(x) = x2 + 3x5 + 4
z(x) = 7x2 + 2x3 – 3

u(x) is a quadratic function.

Step-by-step explanation:

We are asked to choose the correct option that represents a quadratic function.

Since we know that a quadratic function is a second degree polynomial in form .

Upon looking at our given choices we can see that the function represented by option B and D are third degree polynomial, while the function represented by option C is a fifth degree polynomial, therefore, these are not correct choices.  

The polynomial represented by option A is a second degree polynomial and we can rewrite it in standard form of quadratic function as:.

Therefore, option A is the correct choice.

let m = monomial

let t = trinomial

so, m times t = t.

monomial times a trinomial = another trinomial.