Question

Find the zeros of f(x) = 4x 2 + 5x - 21.

A.) {-7/4, 3}
B.) {7/4, -3}
C.) {3/4, -7}

Answer 1

B

Explanation:

using the quadratic formula (formula added) I plugged in all the numbers and solved for x which is the zeros.

Answer 2

The correct choice is B

EXPLANATION

The given function is

`f(x )= 4 {x}^(2) + 5x - 21`

To find the zeros, we equate the function to zero.

`4 {x}^(2) + 5x - 21 = 0`

We split the middle term to get:

`4 {x}^(2) + 12x - 7x - 21 = 0`

Factor by group,

`4x(x + 3) - 7(x + 3) = 0`

Factor further,

`(x + 3)(4x - 7) = 0`

Use the zero product property,

`x + 3 = 0 \: or \: 4x - 7 = 0`

`x = - 3 \: or \: x = (7)/(4)`

Hence the zeros are:

B.) {7/4, -3}