denamontgomery
Sep 23, 2009, 08:52 AM
I am trying to factor a quadratic equation
Unknown008
Sep 23, 2009, 09:13 AM
Ok, I'll give and example: 3x^2+5x-2=0
1. Break down the factors of the term without 'x' and the one with x^2
-2: 1 x - 2 or 2 x -1
3: 1x x 3x
2. Put one set of factors from the first one (-2) with the other set of factors (3) as follows[the factors are put vertically]:
1ooo1xooio| 1x
-2ooo3xooo| -6x
oooooooooo-5x
Now, multiply the horizontal numbers. 1 x 1x = 1x, -2 x 3x = -6x.
Then, add both. 1x + (-6x) = -5x
Now, -5 is not what you're looking for since the term in 'x' in your original equation is +5.
Try with other factors:
-1ooo1xooo| -1x
2ooo3xooio| 6x
oooooooooo5x
Now, you have +5x, which is the good one.
Then, group the diagonal factors in brackets, adding them and putting both groups side by side, don't forget the equal sign and the zero!
(-1+3x)(2+1x) = 0
If you expand this, you should have the original equation back.
Putting the above equation 'cleaner' gives: (3x-1)(x+2)=0
You know that any number multiplied by zero gives zero? Well, that means that either (3x-1) = 0, or (x+2) = 0.
3x-1 = 0
Solve for x to obtain the first answer.
x+2 = 0
Solve for x to obtain the second factor.
The answers for x are 1/3 and -2.
I hope it helped! :)
EDIT: Anyway, that's how I learned it the first time.
ebaines
Sep 23, 2009, 09:17 AM
For a general description of factoring, see:
Factorization - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Factorization)