factoring is my answer right?

B

bronx.system

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Apr 5, 2013
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hey all i started factoring 3 terms and my answers are always flipped compared to book.
Im having trouble knowing what order the + and - signs go.

factor the following

x^2 - 2x - 8

= (x + 2 )(x - 4 )

i understand that its important where the 2 or 4 go because the middle term is a minus -2x but my question is does it matter where the + and - go before the numbers are added.
first step i write
(x ) (x )
then with the + and - i get stuck and end up just placing the numbers where it makes sense.

the book answer was (x - 4)(x + 2)
is that the same as my answer?

a few questions in a row i keep getting the answers flipped compared to book S:

hope that makes sense been up a while brain mushy :confused:
 
Yes, that is the same as your answer- multiplication of numbers is "commutative": ab= ba.
 
bronx.system said:
ooh i see what happened

the book always organises the biggest factors first.
Click to expand...

If the book actually does that, it's only a book convention.

You wrote earlier that the book answer is (x - 4)(x + 2).

x-4 is not "bigger" than x+2, so be careful with phrases like "biggest factor".

Think about this; if you pick any Real number for x, then what you get after subtracting four from it must be smaller than what you would get, were you to add 2, instead.

If, though, you were not talking about the factors themselves, but rather the values -4 and 2, then be careful when using the word "bigger".

-4 is smaller than 2 because -4 lies to the left of 2, on the Real number line. (Remember, numbers get smaller as we move to the left on that line.)

When mathematicians view -4 as having a bigger size than 2, they are talking about magnitudes (distance from zero). You'll learn about this later. Then, the word "bigger" could rightly be used to state that -4 is farther from zero than 2 is, so its 'absolute value' is bigger.

Mainly, I hope that you understand the first comment and realize that the number x+2 is bigger than the number x-4, no matter what value x has. :cool:
 
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