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In the xy-plane, at what two points ...

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Source: — Data Sufficiency |
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by cans » Thu Jun 09, 2011 12:42 am
y=(x+a)(x+b)
intersect x-axis means y=0
thus x=-a,-b
a)a+b = -1
one eqn, 2 variables. insufficient
b)(0,-6) is a point.
thus ab=-6
one eqn, 2 variables. insufficient
a&b together) a+b=-1 ab=-6
a=-3,b=2
points (-3,0) (2,0)
Sufficient
IMO C
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by qduong » Thu Jun 09, 2011 1:01 am
cans wrote: b)(0,-6) is a point.
thus ab=-6
Can you please explain this part ? Thanks
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by phanideepak » Thu Jun 09, 2011 1:58 am
qduong wrote:
cans wrote: b)(0,-6) is a point.
thus ab=-6
Can you please explain this part ? Thanks
case 1 : a+b= -1 so infinite possibilities for a and b
case 2 : -6 = (0+a)(0+b) ab = -6 even here we have many possibilities

case 1 and 2 : only 2 and -3 satisfy the equation

so the two points are(-2,0) and (3,0) Sufficient

answer is C
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by gmatblood » Wed Nov 02, 2011 3:42 am
Is there any alternative way of solving this one?
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