Question

which of the binomials below is a factor of this trinomial? 3x^2 + 18x - 21A. x-1B. x+1C. x+3D. x-3

Answer 1

Answer: A. x –1

Step-by-step explanation

Given

`3x^2+18x-21`

Procedure

To know which is a factor, we have to factorize the latter expression.

0. Number 3 is a common factor between all the terms of the trinomial, then, we can factorize as follows

`=3(x^2+6x-7)`

2. Now, we are left with a trinomial that can be factorized by finding two numbers that when multiplied equals –7, but when added equals 6. For example, 7 and –1:

`7+(-1)=7-1=6`
`7\cdot(-1)=-7`

Verifying that these numbers are correct, we can rewrite our expression as follows:

`=3(x-1)(x+7)`