gmat prep question

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gmat prep question

by jamesk486 » Fri May 11, 2007 6:36 am
In the xy plane, at what two points does the graph of y= (x+a)(x+b)
(1) a+b=-1
(2) the graph intersects the x=axis at at (0,6)

can someone pls pls help me out?

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Re: gmat prep question

by jayhawk2001 » Fri May 11, 2007 1:58 pm
jamesk486 wrote:In the xy plane, at what two points does the graph of y= (x+a)(x+b)
(1) a+b=-1
(2) the graph intersects the x=axis at at (0,6)

can someone pls pls help me out?
Is statement (2) given correctly. I can't visualize a graph
cutting the x-axis at (0,6). If a graph cuts the x-axis, the y intercept
has to be zero. In this case, y = 6 ??

I recall seeing this question on gmat-prep when I took the test and if
I recall correctly, it was something along the lines of

1 - insufficient. We just know a+b=-1. We need to find a and b since
these are the 2 points at which the graph cuts the x-axis

2 - insufficient. We just know ab=6 (substitute for x, y in eqn)

Together we can find a and b and hence is sufficient.

Answer is C.