Which of the following has a factor of [tex]x+2b[/tex], where [tex]b[/tex] is a positive integer constant?

A. [tex]3x^2 + 9x + 18b[/tex]
B. [tex]3x^2 + 24x + 18b[/tex]
C. [tex]3x^2 + 30x + 18b[/tex]
D. [tex]3x^2 + 39x + 18b[/tex]



Answer :

To determine which polynomial has [tex]\(x + 2b\)[/tex] as a factor, we need to factorize each polynomial and see if [tex]\(x + 2b\)[/tex] appears as one of the factors.

### Step-by-Step Factorization:

Option A: [tex]\(3x^2 + 9x + 18b\)[/tex]

We want to check if [tex]\(x + 2b\)[/tex] is a factor.
For [tex]\(x + 2b\)[/tex] to be a factor of [tex]\(3x^2 + 9x + 18b\)[/tex]:
[tex]\[ P(x) = 3x^2 + 9x + 18b \][/tex]

Perform polynomial division to see if [tex]\(x + 2b\)[/tex] into [tex]\(3x^2 + 9x + 18b\)[/tex].

### Option B: [tex]\(3x^2 + 24x + 18b\)[/tex]

Check if [tex]\(x + 2b\)[/tex] is a factor:
[tex]\[ Q(x) = 3x^2 + 24x + 18b \][/tex]

### Option C: [tex]\(3x^2 + 30x + 18b\)[/tex]

Check if [tex]\(x + 2b\)[/tex] is a factor:
[tex]\[ R(x) = 3x^2 + 30x + 18b \][/tex]

### Option D: [tex]\(3x^2 + 39x + 18b\)[/tex]

Check if [tex]\(x + 2b\)[/tex] is a factor:
[tex]\[ S(x) = 3x^2 + 39x + 18b \][/tex]

### Let's derive for each polynomial:

### For [tex]\(P(x) = 3x^2 + 9x + 18b\)[/tex],
If [tex]\(x + 2b\)[/tex] is a factor, then by synthetic division:
[tex]\(P(-2b) = 0\)[/tex]
Substitute [tex]\(x = -2b\)[/tex] in [tex]\(P(x)\)[/tex]:
[tex]\[ 3(-2b)^2 + 9(-2b) + 18b = 12b^2 - 18b + 18b = 12b^2 \][/tex]
Since [tex]\(12b^2 \neq 0\)[/tex], [tex]\(x + 2b\)[/tex] is not a factor.

### For [tex]\(Q(x) = 3x^2 + 24x + 18b\)[/tex],
If [tex]\(x + 2b\)[/tex] is a factor, then by synthetic division:
[tex]\(Q(-2b) = 0\)[/tex]
Substitute [tex]\(x = -2b\)[/tex] in [tex]\(Q(x)\)[/tex]:
[tex]\[ 3(-2b)^2 + 24(-2b) + 18b = 12b^2 - 48b + 18b = 12b^2 - 30b \][/tex]
Since [tex]\( 12b(b - 2.5)\)[/tex], [tex]\(x + 2b\)[/tex] is not a factor.

### For [tex]\(R(x) = 3x^2 + 30x + 18b\)[/tex],
If [tex]\(x + 2b\)[/tex] is a factor, then by synthetic division:
[tex]\(R(-2b) = 0\)[/tex]
Substitute [tex]\(x = -2b\)[/tex] in [tex]\(R(x)\)[/tex]:
[tex]\[ 3(-2b)^2 + 30(-2b) + 18b = 12b^2 - 60b + 18b = 12b^2 - 42b \][/tex]
Since [tex]\( 12b(b - 3.5)\)[/tex], [tex]\(x + 2b\)[/tex] is not a factor.

### For [tex]\(S(x) = 3x^2 + 39x + 18b\)[/tex],
If [tex]\(x + 2b\)[/tex] is a factor, then by synthetic division:
[tex]\(S(-2b) = 0\)[/tex]
Substitute [tex]\(x = -2b\)[/tex] in [tex]\(S(x)\)[/tex]:
[tex]\[ 3(-2b)^2 + 39(-2b) + 18b = 12b^2 - 78b + 18b = 12b^2 - 60b \][/tex]
Since [tex]\( 12b(b - 5b)\)[/tex], [tex]\(x + 2b\)[/tex].

### The right polynomial is
[tex]\[ \boxed{3} \][/tex]