I need help with algebra?

There several ways of handling these. I will demonstrate the FOIL method.


(F)irst Terms: x*x = x²
(O)uter Terms: -8*x = -8x
(I)nner Terms: -5*x = -5x
(L)ast Terms: -5*-8 = 40

Sum of Terms: x² - 8x - 5x + 40

= x² - 13x + 40

I never heard of FOIL until I started teaching. Go Figure!

Add on: (May 23, 08 Time: 10:37AM EST)
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Here is another way of doing this problem:

http://www.scs.gmu.edu/~mwester1/solution1.pdf

(x - 5)(x - 8)
= x*x - 5*x - x*8 + 5*8
= x^2 - 5x - 8x + 40
= x^2 - 13x + 40

FOIL is a memory crutch/reminder to make sure you do ALL the feasible multiplications when multiplying one binomial by another.

There are 4 possible multiplications (a 2-term times a 2-term yields 4 product terms). Were you multiplying a trinomial times a trinomial you would have 9 multiplications. When the multiplications get lengthier (like the trinomial times a trinomial) sometimes doing the multiplication like conventional multiplication will help you keep the like/similar terms column-grouped together; that makes combining/collecting them easier.

FOIL means First, Outer, Inner , Last
refers to the order in which you multiply the terms of binomials.

So FIRST --

in your example (x-5) (x-8)

the First terms are the 2 Xs

so X*X = X^2 (x squared)

now - OUTER
the 2 outer terms are the x from the 1st binomial and the -8 from the 2nd binomial

multiply them together and you get -8x

INNER : multiply the 2 inner terms (-5) * (x)
and you get -5x

Finally : LAST - you multiply the Last terms of each binomial
in this case it would be (-5)*(-8)
= 40

Now you simply add them all up

x^2 -8x -5x + 40 (ok?)

Now you can simplify by combining like terms - the Xs

-8x-5x = - 13x

so x^2-13x+40 is your final answer

first outer inner last

(x - 5)(x - 8)

take the two first digits in the brackets: x multiplyed by x is x^2

outer: the first x and the last 8
x multiplyed by NEGATIVE8 = NEGATIVE8x (-8x)

inner: the NEGATIVE5 multiplyed by the second x

-5 multiplyed by x = NEGATIVE5x (-5x)

last: NEGATIVE5 multiplyed by NEGATIVE8 = POSITIVE40

add all the same values together- as in all the ^2, all the ^1 and the numbers

x^2 + (-5x + (-8x)) + 40

= x^2 -13x + 40

simple :)

Foil...
First two terms: x * x = x^2
Outer two terms: x * (-8) = -8x
Inner two terms: (-5) * x = -5x
Last two terms: (-5)(-8) = 40
(x-5)(x-8) = x^2 - 13x +40

it the distrubitive proptery

How old are you? ;)

FOIL: First, Outer, Inner, Last
( x - 5 ) ( x - 8 )
The first term of (x-5) is x
The last term of (x-5) is 5
The first term of (x-8) is x
The last term of (x-8) is 8

Outer terms are the ones on the ends.
(x from x-5, and -8 from x -8)
Inner terms are the ones in the middle.
( -5 from x-5, and x from x-8)

The FIRST terms multiplied together:
x * x = (x)(x) = x²

The OUTER terms multiplied together:
x * (-8) = -8x

The INNER terms multiplied together:
(-5) * x = -5x

The LAST terms multiplied together:
(-5) * (-8) = 40

Add them all up:
x² - 8x - 5x + 40
x² - 13x + 50

So, you end up with
( x - 5 ) ( x - 8 ) = x² - 13x + 50