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.
x2x72=0
(x9)(x8)=0
so the answer is D
8,9

Geometry  Reiny, Saturday, September 5, 2009 at 10:53pm
no, your factors should have been
(x9)(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
(2x1)(3x5) = 0
(3x1)(2x5) = 0
(6x1)(x5) or
(x1)(6x5) = 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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