XY Plane

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XY Plane

by LSB » Tue Aug 26, 2008 12:38 pm
I picked e because I was rushed. Whenn I tried to redo the question I multiplied out the brackets and plugged in 0 for X. This left me with a+b. Statement 1 defines a+b. So, Iwould say answer A should be the correct answer. What value does statement 2 add?
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XY Plane

Master | Next Rank: 500 Posts
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by LSB » Thu Aug 28, 2008 1:35 am
Anybody on this?

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by ankur_arora » Thu Aug 28, 2008 2:37 am
IMO C..

As the equation represents a parabola that intersects x axis twice and y axis once.

the equation from question : y = x(x) + x(a+b)+ab
for it to intersect x axis we need a and b both

so the equation on substituting 0 for y becomes x(x) + (a+b)x +ab=0
this is a quadratic enq with roots -a and -b and can be written as:
x(x) - (-a-b) +ab=0
or
x(x) +x(Sum of roots)+ product of roots=0

1) provides -> sum of roots
2) provides -> product of roots

so answer is C :)

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by ankur_arora » Thu Aug 28, 2008 3:06 am
modification to the earlier post::

the product is -ve so a and b differ in sign

a+b=-1 and ab=-6

=> a=-3 and b=2 or a=2 and b=-3
we get the two points ;)