Question

Factor x3 – 4x2 + 7x – 28 by grouping. What is the resulting expression?

(x2 – 4)(x + 7)
(x2 + 4)(x – 7)
(x2 – 7)(x + 4)
(x2 + 7)(x – 4)

Answer 1

x^3 -4x^2 +7x -28 = x^2(x-4) +7(x -4) = (x^2 +7)(x-4)

so the 4th choice will be right sure

Answer 2

Consider polynomial
`x^3 - 4x^2 + 7x - 28.` You can group first two terms and last two terms:

`x^3 - 4x^2 + 7x - 28=(x^3 - 4x^2) + (7x - 28).`

In first brackets the common factor is
`x^2` and in second brackets the common factor is 7, then

`x^3 - 4x^2 + 7x - 28=(x^3 - 4x^2) + (7x - 28)=x^2(x-4)+7(x-4)=(x-4)(x^2+7).`

Answer: the correct answer is D.