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# In the xy-plane, at what two points does the graph of y =

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Senior Manager
Joined: 24 Mar 2011
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In the xy-plane, at what two points does the graph of y =  [#permalink]

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23 Apr 2011, 14:35
3
00:00

Difficulty:

45% (medium)

Question Stats:

72% (01:05) correct 28% (01:30) wrong based on 130 sessions

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In the xy-plane, at what two points does the graph of y = (x+a)(x+b) intersect the x-axis?

(1) a+b = -1
(2) the graph intersect the y-axis at (0,-6)

OPEN DISCUSSION OF THIS QUESTION IS HERE: http://gmatclub.com/forum/in-the-xy-pla ... 88398.html

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Joined: 14 Feb 2011
Posts: 175
Re: In the xy-plane, at what two points does the graph of y =  [#permalink]

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23 Apr 2011, 15:11
agdimple333 wrote:
In the xy-plane, at what two points does the graph of y = (x+a)(x+b) intersect the x-axis?

(1) a+b = -1
(2) the graph intersect the y-axis at (0,-6)

Clearly the graph intersects at (-a,0) and (-b,0), so we need to find value of a and b.

Statement 1 gives a+b = -1, so not sufficient

Statement 2 says that y = -6 when x is 0 or ab=-6, so not sufficient.

Combining 1 and 2, we can get that a and b are -3 and 2 respectively, so sufficient.
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Re: In the xy-plane, at what two points does the graph of y =  [#permalink]

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24 Apr 2011, 21:09
1
y = (x+a)(x+b) intersect the x-axis when y = 0, which happens when x = -a or x = -b

=> 0 = (x+a)(x+b)

x^2 + x(a+b) + ab = 0

(1) gives us value of (a+b), but not that of ab

So insufficient.

(2) says

-6 = (0+a)(0+b) => ab = -6

Does not give us value of (a+b), so insufficient.

(1) and (2) give x^2 -x - 6 = 0

(x-3)(x+2) = 0

=> x = 3, -2

Sufficient

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Re: In the xy-plane, at what two points does the graph of y =  [#permalink]

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15 Aug 2017, 09:24
st 2 tells that the peak of the parabol is fixed, and st 1 indicates that the intersected points are fixed => C is the answer. There is no need to check whether the values of the equatation.
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Joined: 02 Sep 2009
Posts: 50583
Re: In the xy-plane, at what two points does the graph of y =  [#permalink]

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03 Oct 2017, 08:19
agdimple333 wrote:
In the xy-plane, at what two points does the graph of y = (x+a)(x+b) intersect the x-axis?

(1) a+b = -1
(2) the graph intersect the y-axis at (0,-6)

OPEN DISCUSSION OF THIS QUESTION IS HERE: http://gmatclub.com/forum/in-the-xy-pla ... 88398.html

OPEN DISCUSSION OF THIS QUESTION IS HERE: http://gmatclub.com/forum/in-the-xy-pla ... 88398.html

--== Message from the GMAT Club Team ==--

THERE IS LIKELY A BETTER DISCUSSION OF THIS EXACT QUESTION.
This discussion does not meet community quality standards. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.

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Re: In the xy-plane, at what two points does the graph of y = &nbs [#permalink] 03 Oct 2017, 08:19
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