powerprep question

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jc114: Senior | Next Rank: 100 Posts; Posts: 53; Joined: Thu Apr 12, 2007 12:32 am; Thanked: 1 times

by jc114 » Sat May 12, 2007 7:50 am

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 intersects the x=axis at at (0,6)

i chose E but the answer is c

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Source: Beat The GMAT — Data Sufficiency | Sat May 12, 2007 7:50 am

f2001290: Master | Next Rank: 500 Posts; Posts: 400; Joined: Sat Mar 10, 2007 4:04 amFollowed by: 1 member; Thanked: 1 times

by f2001290 » Sun May 13, 2007 5:31 am

When a line intersects X axis, y = 0

1. y = x^2 + (a+b)x + ab - not sufficient

2. Substitute (0,6) in the equation, we get the value of ab.

Using both the statements

x^2 - x + 6 = 0

we can get two values of x by solving this equation

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jc114: Senior | Next Rank: 100 Posts; Posts: 53; Joined: Thu Apr 12, 2007 12:32 am; Thanked: 1 times

by jc114 » Sun May 13, 2007 2:27 pm

but then if there are 2 answers for x isn't it then E?

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f2001290: Master | Next Rank: 500 Posts; Posts: 400; Joined: Sat Mar 10, 2007 4:04 amFollowed by: 1 member; Thanked: 1 times

by f2001290 » Mon May 14, 2007 4:42 am

Read the question carefully, it asks for two points.

If x1 nad x2 are the values of x, then (X1,0) and (x2,0) are my points

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