In the xy-plane, at what two points does the graph of

[cml]

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)

I'm having problems finding one solution for x when y is 0.

We are asked to value of x when y is zero.

First I distributed the equation above and got:
y=x^2+x(b+a)+ab

(1) Alone
y=x^2+x(-1)+ab

We do not have the value for ab so we cannot find the value of x when y is 0. INSUFFICIENT

(2) Alone gives us the value of the y-intersect - y=(0+a)(0+b)=ab
So ab=-6 INSUFFICIENT

Together I got

y=x^2+x(-1)+(-6), we make y=0 to find the x-intersect
0=x^2+x(-1)+(-6)
0=(x-3)(x+2)

So we have two answers for x. Therefore it should be E. I got this correct during the exam but really didn't know why, and still don't.

Cheers!

[RonPurewal]

Please try to search the forum before posting. Just about every GMAT Prep problem has already been discussed extensively.

Check out the question part again: At what two points...?
I.e., if you can identify the two points, that's sufficient. It doesn't matter which of the two points you decide to call "x".