How to factor a trinomial by getting rid of the impostor
Learn how to factor a trinomial of the form ax
^{2} + bx + c when a is not equal to 1 by getting rid of the "impostor"
The impostor here is a, or the coefficient of ax
^{2} . The impostor will show itself in the factored form as
a( )( ) or b( )c( ) if a = bc
This method is straightforward and does not involve too much trial and error and that is why I like it. The best way to understand what we mean by getting rid of the impostor or a is to solve some examples. Here are 3 great examples that will show you how to factor a trinomial quickly.
Example 1: 3x
^{2} + 7x + 2
For this example, the impostor that we will eventually get rid of is 3.
Step 1
Factor any GCF if any. Since 3x
^{2} + 7x + 2 does not have any GCF, go to step 2.
Step 2
Multiply a by c.
a × c = 3 × 2 = 6
Step 3
Factor as if a = 1 using (3x + blank)(3x + blank) as your factored form. Then, ask what multiplies to 6 and adds up to 7.
Notice how we used 3x as the first term in each factor! This is the way to do it every time.
Since 1 × 6 = 6 and 1 + 6 = 7, use 1 and 6 to fill in the blank.
We get (3x + 1)(3x + 6)
Step 4
Pull out impostor by GCF and banish. In other words, using (3x + 1)(3x + 6), factor out the GCF for each factor.
(3x + 1)(3x + 6) = (3x + 1)×3(x + 2)
As you can see, the impostor is the 3, so banish it.
After banishing or getting rid of the impostor which is 3, the final answer is (3x + 1)(x + 2)
Example 2: 8x
^{2}  10x  3
For this example, the impostor that we will eventually get rid of is 8.
Step 1
Factor any GCF if any. Since 8x
^{2} 10x 3 does not have any GCF, go to step 2.
Step 2
Multiply a by c.
a × c = 8 × 3 = 24
Step 3
Factor as if a = 1 using (8x + blank)(8x + blank) as your factored form. Then, ask what multiplies to 24 and adds up to 10.
Notice again how we used 8x as the first term in each factor!
Since 12 × 2 = 24 and 12 + 2 = 10, use 12 and 2 to fill in the blank.
We get (8x + 12)(8x + 2)
Step 4
Pull out impostor by GCF and banish. In other words, using (8x + 12)(8x + 2), factor out the GCF for each factor.
(8x + 12)(8x + 2) = 4(2x + 3)×2(4x + 1)
As you can see, the impostor is split up into two of its factors, so banish it by multiplying the two numbers to get your real impostor, 8.
After banishing or getting rid of the impostor which is 8, the final answer is (2x + 3)(4x + 1)
How to factor a trinomial when there is a GCF in step 1
Example 3: 6x
^{2} + 8x + 2
Step 1
Factor the GCF if any. GCF = 2, so 6x
^{2} + 8x + 2 = 2(3x
^{2} + 4x + 1 )
Step 2
Be careful here. The impostor is 3 since we need to factor 3x
^{2} + 4x + 1.
Multiply a by c.
a × c = 3 × 1 = 3
Step 3
Factor as if a = 1 using (3x + blank)(3x + blank) as your factored form. Then, ask what multiplies to 3 and adds up to 4.
Since 3 × 1 = 3 and 3 + 1 = 4, use 3 and 1 to fill in the blank.
We get (3x + 1)(3x + 3)
Step 4
Pull out impostor by GCF and banish. In other words, using (3x + 1)(3x + 3), factor out the GCF for each factor.
(3x + 1)(3x + 3) = (3x + 1)×3(x + 1)
After banishing the impostor, we get (3x + 1)(x + 1)
However, do not forget the factor in step 1, so the final answer is 2(3x + 1)(x + 1)

Nov 15, 18 05:01 PM
Modeling multiplication with number counters  Learning multiplication is fun!
Read More
New math lessons
Your email is safe with us. We will only use it to inform you about new math lessons.