Coordinate Geomertry

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Please can some one help me understand why the answer is C?

[Mani_mba]

y = (x+a)(x+b)
y = x^2 + x(a+b) + ab ---> ST1

If we look at statement 1, a+b = -1
So the eqn becomes y = x^2 - x + ab

This is insufficient as a and b are unknown...

Look at statement 2, the curve intersects y -axis at (0,-6)
Substituting these values in ST1, we imply ab=-6. But still this is insufficient as a+b is unknown.

Combining statement 1 and 2, we get y = x^2 -x -6
In x axis , y = 0. So x^2 -x -6 = 0
x = 3,-2.. The points are (3,0) and (-2,0)

Hence C.

[cubicle_bound_misfit]

Hi,
I had no idea that Vue gives second degree equation for Co ordinate in GMAT exam.

Ian, if possible Please put some light on that.

But for this problem,

X-axis intersect will happen when y=0 i.e. (x+a)(x+b)=0

so we need to find value for both a and b which is possible when we combine both the stmt.

Ans C.

regards,

[Ian Stewart]

Hi,
I had no idea that Vue gives second degree equation for Co ordinate in GMAT exam.

Ian, if possible Please put some light on that.

\
regards,

Yes, you can certainly see second degree equations- and a lot of other kinds of equations- in GMAT co-ordinate geometry, but you don't need to know much about them. The question above is typical; you need to know how to find x-intercepts (set y = 0), but you don't even need to know that the equation represents a parabola. As long as you know the basics in co-ordinate geometry - equations for lines, what the slope means, how to find x and y intercepts, how to calculate distances, how to graph things, etc - you should be fine; no need to learn the equations for ellipses or hyperbolas or anything like that.