Answer:
(x + 2)(-8x + 1) or,
(-8x + 1)(x + 2)
Step-by-step explanation:
To factor quadratic equations in the form ax² + bx + c that cannot be factored in your head, the first step is to find factors for the product of coefficient a and constant c whose sum equates to coefficient b. This may sound confusing, but it is easier in practice.
So, we find the product of -8 and 2 which is -16.
Now we list the factors of -16. I like to list them as factor pairs. These are:
1, -16, 2, -8, 4, -4, 8, -2, 16, -1
Next, we examine which combination of factor pairs has a sum of -15. These are -16 and 1. To check: -16 + 1 = -15
Then, we place these values as coefficients into the original equation as substitutes for -15x and find factor out the greatest common factor (GCF) of the equation terms:
-8x² - 16x + x + 2
(-8x² - 16x) + (x + 2)
The GCF between -8x² and -16x is -8x. The GCF between x and 2 is 1.
-8x(x + 2) + 1(x + 2)
If these binomials within the parenthesis match, then you have found the factors. The binomial within the parenthesis is one factor and the GCFs outside of each binomial are is the other factor. Thus, the factors of the original quadratic expression are:
(-8x + 1)(x + 2)
To check these factors for accuracy, we can use the FOIL method to expand the expression, combine like terms, and observe if it matches the original equation. FOIL stands for Firsts, Outsides, Insides, and Lasts, instructing which terms of each binomial are multiplied together.
Firsts: -8x(x) = -8x²
Outsides: -8x(2) = -16x
Insides: 1(x) = x
Lasts: 1(2) = 2
In an equation: -8x² - 16x + x + 2 → -8x² - 15x + 2
This is the original equation, therefore (-8x + 1)(x + 2) are accurate factors.