Question

What are the factors of 5x2 + 39x − 8?

Answer 1

Answer:

C. (5x - 1)(x + 8)

Step-by-step explanation:

In a factoring problem by hand, the common steps to solve would be the "AM" method, or (Add-Multiply). Simply stated, finding what adds to the x-coeficient and what multiplies to the constant. In this case, what adds to 39(x) and what multiplies to 8. Just reading that, we can see that there aren't any numbers that can do that, so we have to improvise. Set up the problem equal to something that it can factor into:

1. Multiply the 5 and -8 = -40: this is what we will factor
2. The factors with add to 39 are 40 and -1.
3. Set up the problem:

$5x^{2}+39x-8 = 5x^{2}+40x-x-8$

Now, we can fo the math:

$5x^{2} -8 = 5x^{2} -8$

8(5x - 1) + x(5x - 1)

Factor (5x - 1) from this:

(5x - 1)(x + 8)

And we have our answer.