Answer: A. x –1
Explanation
Given
[tex]3x^2+18x-21[/tex]
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
[tex]=3(x^2+6x-7)[/tex]
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:
[tex]7+(-1)=7-1=6[/tex][tex]7\cdot(-1)=-7[/tex]
Verifying that these numbers are correct, we can rewrite our expression as follows:
[tex]=3(x-1)(x+7)[/tex]
