Posted by **Emory** on Saturday, September 5, 2009 at 10:28pm.

Solve the quadratic equation.

13) x2 - x = 72

A) -8, 9

B) -8, -9

C) 1, 72

D) 8, 9

Can some one please check my answer and let me know if I did it the right way.

x2-x-72=0

(x-9)(x-8)=0

so the answer is D

8,9

- Geometry -
**Reiny**, Saturday, September 5, 2009 at 10:53pm
no, your factors should have been

(x-9)(x+8) = 0

so x=9 or x=-8 which would be A

- Geometry -
**Emory**, Saturday, September 5, 2009 at 10:56pm
Well you see that was how I did at first but I was not too sure about it so then I got it right the first time I always get confused with that any tips to remind me next time. Thanks

- Geometry -
**Reiny**, Saturday, September 5, 2009 at 11:03pm
After you factor, you should multiply it back out to see if you end up with the original.

I knew immediately that your factors were wrong.

Both your factors ended with negatives for the constants, so your last term would have been positive, but it was -72

- Geometry -
**Emory**, Saturday, September 5, 2009 at 11:09pm
Oh,I see thank you I have another one for you that I don't know how to start it and it goes like this 6y2 = 7y - 5?

Can you please help me just to start it off

- Geometry -
**Reiny**, Saturday, September 5, 2009 at 11:35pm
put everything to one side

6y^2 - 7y + 5 = 0

I see a positive at the end, which tells me that the signs are the same, looking at the middle term they must be both negative.

so it must be (?x - 1)(?x - 5) = 0

only 4 possibilies are

(2x-1)(3x-5) = 0

(3x-1)(2x-5) = 0

(6x-1)(x-5) or

(x-1)(6x-5) = 0

unfortunately none of these give us a middle term of -7y

so your question does not factor.

- Geometry -
**Emory**, Saturday, September 5, 2009 at 11:45pm
So then the answer is 0 because like you mention there is no factor "correct"

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