Graphs point of intersectoin

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gmatrant: Master | Next Rank: 500 Posts; Posts: 416; Joined: Wed Oct 03, 2007 9:08 amFollowed by: 1 member; Thanked: 10 times

by gmatrant » Wed Nov 14, 2007 1:14 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 y axis at (0,-6)

OA is C

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Source: Beat The GMAT — Problem Solving | Wed Nov 14, 2007 1:14 am

camitava: Legendary Member; Posts: 645; Joined: Wed Sep 05, 2007 4:37 amFollowed by: 5 members; Location: India; Thanked: 34 times

by camitava » Wed Nov 14, 2007 1:32 am

Gmatrant, as the line crosses the X-axis, so y = 0 and (x + a)(y + b) = 0
So x = -a and -b :- These are the points thru which that equ has passed thru X-axis. But we have to calculate the value of a and b. And that can be done by statement - 2. As, -6 = (0 + a)(0 + b) or ab = -6
And by statement - 1, a + b = -1
From these two questions, we can easily solve the values of a and b. So IMO C.

Correct me If I am wrong

Regards,

Amitava

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gmatguy16: Master | Next Rank: 500 Posts; Posts: 124; Joined: Thu Aug 23, 2007 5:11 am; Thanked: 2 times

by gmatguy16 » Wed Nov 14, 2007 4:22 pm

agree with amit. ans c

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