SOLUTION: Find all factors of x^2+x-12

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Question 182224: Find all factors of x^2+x-12
Found 2 solutions by Alan3354, josmiceli:
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
Find all factors of x^2+x-12
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Having the coeff of x^2 = 1 makes it simpler.
Any factors will be
(x +- ?)*(x +- ?)
Only the two numbers that multipy to be -12 are a mystery.
There are a few possibilities:
1 & 12
2 & 6
3 & 4
That's all
Since it's -12, one will be negative and one positive.
Since there's 1x, the positive number will be 1 more than the negative number.
Also, since there's 1x, the 2 numbers differ by 1.
Only 3 & 4 fit.
So it's +4 and -3.
(x+4)*(x-3)

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
x%5E2+%2B+x+-+12
If I set the equation equal to 0, I can use
the method of completing the square which says:
Take 1/2 of the coefficient of x, square it,
and add it to both sides
First, add 12 to both sides
x%5E2+%2B+x+-+12+=+0
x%5E2+%2B+x+=+12
x%5E2+%2B+x+%2B+%281%2F2%29%5E2+=+12+%2B+%281%2F2%29%5E2
x%5E2+%2B+x+%2B+1%2F4+=+12+%2B+1%2F4
%28x+%2B+1%2F2%29%5E2+=+49%2F4
Take the square root of both sides
x+%2B+1%2F2+=+7%2F2
x+=+6%2F2
(a) x+=+3
Also I take the negative square root
x+%2B+1%2F2+=+-%287%2F2%29
x+=+-%288%2F2%29
(b) x+=+-4
Subtract 3 from both sides of (a)
x+-+3+=+0
Add 4 to both sides of (b)
x+%2B+4+=+0
Since these are both 0, their products is 0
%28x+-+3%29%28x+%2B+4%29+=+0
x%5E2+%2B+x+-+12+=+0
The factors are x-3 and x%2B4