Question

Factor completely
4x^2 - 18x - 36

Answer 1

2(x - 6)(2x + 3)

Explanation:

There are a few steps to factoring depending on the polynomial.

Step 1. Factor our a common factor if possible.

Every term is divisible by 2, so factor out a 2.

4x^2 - 18x - 36 =

= 2(2x^2 - 9x - 18)

Step 2. We need to factor the quadratic trinomial.

Now we have a quadratic trinomial, in which the x^2 term is not plain x^2, but it has a coefficient of 2.

Our polynomial is of the form ax^2 + bx + c, with "a" not equal to 1.

We have 2x^2 - 9x - 18, so we have a = 2, b = -9, c = -18.

We can try guessing, but instead, I will use the "ac" method.

Step A. Multiply coefficients ac:

ac = 2(-18) = -36

Step B. Now we need two numbers that add to b and multiply to ac.

We need two numbers that add to -9 and multiply to -36.

The numbers are -12 and 3 since (-12)(3) = -36, and -12 + 3 = -9.

We now break up the middle term, -9x, using these two numbers.

= 2(2x^2 - 12x + 3x - 18)

Now we factor by grouping. Factor a common factor out of the first two terms, and factor a common factor out of the last two terms.

= 2[2x(x - 6) + 3(x - 6)]

x - 6 is a common factor inside the brackets, so we factor it out inside the brackets.

= 2[(x - 6)(2x + 3)]

= 2(x - 6)(2x + 3)

Answer 2

Answer: 2(2x + 3)(x - 6)

Step-by-step explanation: For any factoring problem you do, your first

task will be to determine if a GCF exists for the original polynomial.

If a GCF does exist, it must be factored out as the first step to the problem.

In the problem you see here, the 3 terms in

the original polynomial have a GCF of 2.

So a 2 must be factored out as your first step.

This leaves you with 2(2x² - 9x - 18).

This does not make your life a whole lot easier however

because you still have a coefficient on the x squared term.

Factoring from here, you get 2(2x + 3)(x - 6).