# Geometry

posted by on .

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
8,9

• Geometry - ,

no, your factors should have been
(x-9)(x+8) = 0

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

• Geometry - ,

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 - ,

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 - ,

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?

• Geometry - ,

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 - ,

So then the answer is 0 because like you mention there is no factor "correct"