Thread: Help with FOIL

1. Help with FOIL

$\displaystyle (2x - 1)(1x - 4)$

The answer is 2x^2 -9x + 4 but I dont know how to arrive at this answer, could some one please walk me through this .

2. F First term
O Outer term
I Inner term
L last term

So

$\displaystyle 2x^2 -8x -1x - (-4)$ so $\displaystyle 2x^2 - 9x +4$

3. The best help you can receive with FOIL is to forget it and simply learn to multiply.

You have two factors: (2x-1) and (x-4)

Each factor has two terms.

(2x-1) has '2x' and '-1'
and
(x-4) has 'x' and '-4'.

Multiply each term from each factor with each term from the other factor. Keep track so you don't miss any and don't do any twice.

(2x)*(x)
(2x)*(-4)
(-1)*(x)
(-1)*(-4)

"FOIL" is a cute idea to keep track of 2x2 multiplication. If you learn to keep track yourself, you never need to think about it again.

4. Originally Posted by allyourbass2212
$\displaystyle (2x - 1)(1x - 4)$

The answer is 2x^2 -9x + 4 but I dont know how to arrive at this answer, could some one please walk me through this .
You may understand the distribution method better, and then learn FOIL as 'cmf' suggested. FOIL is just another way to multiply binomials. Some like it, some don't. It's your choice. Here's how you would use the distributive property to achieve the same result.

$\displaystyle (2x-1)(1x-4)$

Distribute the 2x and -1 from the first binomial over the second binomial, combine like terms and voila!:

$\displaystyle 2x(1x-4)-1(1x-4)$

$\displaystyle 2x^2-8x-1x+4$

$\displaystyle 2x^2-9x+4$

5. Hi,

I didn't know this method FOIL ^^

-------------------
By the way, I'd suggest you doing this way... :

$\displaystyle (2x-1)(x-4)$

Imagine that $\displaystyle a=x-4$
You will get $\displaystyle (2x-1)a$
Using the basics of multiplication expanding, this is equal to :

$\displaystyle (2x)*a-1*a$

Substituting back :

$\displaystyle =(2x)(x-4)-1*(x-4)$

Using again this expansion :

$\displaystyle =(2x)*x-(2x)*4-(x-4)=...$

Edit : masters of rapidity... :P

6. 2Xsquared-8X-X+4
collect like terms

2Xsquared-9X+4

andrew