Question

Which represents a quadratic function? f(x) = −8x3 − 16x2 − 4x f (x) = three-quarters x 2 + 2x − 5 f(x) = StartFraction 4 Over x squared EndFraction minus StartFraction 2 Over x EndFraction + 1 f(x) = 0x2 − 9x + 7

Answer 1

Answer:

$2.\ f(x) = \frac{3}{4}x^2 + 2x - 5$

Step-by-step explanation:

Given

$f(x) = -8x^3 - 16x^2 - 4x\\f(x) = \frac{3}{4}x^2 + 2x - 5\\f(x) = \frac{4}{x^2} - \frac{2}{x} + 1\\f(x) = 0x^2 - 9x + 7$

Required

Which of the above is a quadratic function

A quadratic function has the following form;

$ax^2 +bx + c = 0 \ where \ a\neq 0$

So, to get a quadratic function from the list of given options, we simply perform a comparative test of each function with the form of a quadratic function

$1.\ f(x) = -8x^3 - 16x^2 - 4x$

This is not a quadratic function because it follows the form $f(x) = ax^3 + bx^2 + c$ and this is different from $ax^2 +bx + c = 0 \ where \ a\neq 0$

$2.\ f(x) = \frac{3}{4}x^2 + 2x - 5$

This function has an exact match with $ax^2 +bx + c = 0 \ where \ a\neq 0$

By comparison; $a = \frac{3}{4}\ b = 2\ and\ c = -5$

$3.\ f(x) = \frac{4}{x^2} - \frac{2}{x} + 1$

This is not a quadratic function because it follows the form $f(x) = \frac{a}{x^2} + \frac{b}{x} + c$ and this is different from $ax^2 +bx + c = 0 \ where \ a\neq 0$

$4.\ f(x) = 0x^2 - 9x + 7$

This is not a quadratic function because it follows the form $f(x) = ax^2 +bx + c = 0\ but\ a = 0$

Unlike the quadratic function where $a\neq 0$

So, from the list of given options, only $2.\ f(x) = \frac{3}{4}x^2 + 2x - 5$ satisfies the given condition