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# Solve by factoring; x2 – 9x = -20?

by Harsh
Member since:
November 03, 2008
Total points:
1,400 (Level 3)

## Best Answer - Chosen by Voters

x^2-9x=-20

x^2-9x+20=0

x^2-5x-4x+20=0

x(x-5)-4(x-5)=0

(x-4)(x-5)=0

=> Factors are
(x-4)(x-5)
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• by tonyc4l
Member since:
December 20, 2008
Total points:
756 (Level 2)
First add 20 to both sides, so the equation reads x^2 - 9x + 20 = 0. Since this is a quadratic, you expect to be able to factor it into (x+a)(x+b) = 0. You're trying to find a and b so that a + b = -9 and ab = 20. From looking at it and trying different numbers, you should get -4 and -5. (-4 + -5 = -9 and -4 * -5 = 20). So the factorization is (x-4)(x-5) = 0.
Now the only way for a product of two factors to equal zero is for one or both of them to be zero. That is, x-4 = 0 or x-5 = 0. If you solve these equations, you get x=4, x=5 as solutions.
• by aaron l
Member since:
October 17, 2008
Total points:
630 (Level 2)
Get all numbers on 1 side and make the equation = 0:
x2-9x+20
Then factor everything out like normal:
(x-4)(x-5)
If you want to solve for x, all you have to do is make one parenthesized equation 0 so you would either have 4 as x or 5 as x
x=4 or 5 to make the equation 0 Plug it in!
• by megavinx
Member since:
August 25, 2006
Total points:
3,151 (Level 4)
Transpose -20:

x2 - 9x + 20 = 0; from here you can factor out.

(x - 5)(x - 4) = 0; set both factors to zero.

x - 5 = 0 ; x - 4 = 0

Therefore the two roots are: x = 5 and x = 4.
• by ɷḧello
Member since:
August 27, 2007
Total points:
6,261 (Level 5)
x^2-9x=-20

x^2-9x+20=0

Factor:
(x-4)(x-5)
• by Erik
Member since:
March 03, 2009
Total points:
8,805 (Level 5)
x^2 - 9x + 20 = 0

(x - 4) * (x - 5)
• by Maria
Member since:
December 12, 2013
Total points:
111 (Level 1)
factor x^2-2x-15