DS problem - graph

gmatme · Posted: Sun Mar 18, 2007 9:24 am Post subject: DS problem - graph

How the first statement is sufficient?

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)

Ans is C ?

jayhawk2001 · Posted: Sun Mar 18, 2007 9:39 am Post subject:

1 - insufficient. All we have it x^2 -x + ab = 0. Cannot
solve for x

2 - insufficient. y = x^2 + (a+b)x + ab implies ab = -6. Cannot
solve for x

Using 1 and 2

x^2 - x - 6 = 0
x = 3 & -2

So, C looks like the correct answer

gmatme · Posted: Sun Mar 18, 2007 9:56 am Post subject:

Can you please explain why ab = -6?

gmatme · Posted: Sun Mar 18, 2007 10:23 am Post subject:

I know why ab=-6, please ignore my last post.