Factoring Expressions: x^2 + 4x - 21

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xwintersnight

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Nov 12, 2007
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I've tried looking at the tutorials and everything, but I'm still completely confused. I wasn't able to be in class today, so the teacher gave me the homework before I left. So, I'm completely clueless. We're supposed to "factor the expression. If the expression cannot be factored, say so", but I'm still confused. Factoring wasn't my strongpoint in Algebra 1. So, here's my first problem:

x[sup:2wve24l9]2[/sup:2wve24l9] + 4x - 21

I have no work, because I don't know what I'm supposed to do. If someone could explain to me and show me how I'm supposed to do these sorts of problems, I will be eternally grateful.
 
Re: Factoring Expressions

x2 + 4x - 21

Okay, here's what you have to do.
It's a two termed expression because it's x squared.
So, start your problem off like this.
(x ) (x )

The middle, 4x, and the 21 go together, in a way.
You have to find two numbers that multiplied make 21,
but at the same time can subract to make 4.
(The only reason it's subtract to make 4 in this problem
is because of the minus sign in front of the 21. That sign
will tell you whether the two numbers should add or
subract to give you the middle number.)

You're numbers in this case are 7 and 3.
7 times 3 equals 21.
7 minus 3 equals 4.

I don't exactly remember all the rules with the signs,
but I believe it should look like this:
(x-7) (x-3)

I wouldn't swear on it because it's been awhile,
but I think that's right.
 
Re: Factoring Expressions

Well, thanks for the help, Hollis and Denis. I {think} it made sense... ^^
 
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