Question

Factor the trinomial: 4x2 - 8x - 5
A. (2x + 1)(2x - 5)
B. (4x + 1)(x - 5)
C. (4x - 5)(x + 1)
D. prime

Answer 1

Since you're given the answer choices, you can FOIL each choice out and see which one gives you the original expression

Answer 2

so what do you get when you foil something like (4x - 5)(x + 1) out (I'm just picking at random)?

Answer 3

the only thing i know how to foil is leftovers

Answer 4

very clever lol, ok I'll show you how to expand out (4x - 5)(x + 1)

(4x - 5)(x + 1)

is the same as

4x(x + 1) - 5(x + 1)

then you distribute that to get

4x*x + 4x*1 - 5*x - 5*1

and that turns into

4x^2 + 4x - 5x - 5

and finally you combine like terms to get

4x^2 - x - 5

Answer 5

so (4x - 5)(x + 1) turns into 4x^2 - x - 5

this is NOT the original expression, so choice C is out

Answer 6

use the same steps to expand the other choices

Answer 7

im leaning towards A?

Answer 8

that's a great place to lean, is that a guess or have you eliminated B (or expanded out A to get the original expression)?

Answer 9

the answer is definitely A, I just want to make sure you see how it is choice A

Answer 10

i just expanded it. i understand this foil situation now

Answer 11

ok that's great, remember that FOIL stands for

F: First
O: Outer
I: Inner
L: Last

this page explains it in more detail:
http://www.mathwarehouse.com/algebra/polynomial/foil-method-binomials.php