Hey everybody,

this forum has helped me immensely in analyzing my wrong answers on the

GMATprep tests. I have not found an explained answer to this question yet, so here we go:

In the xy-coordinate plane, the graph of \(y=x^2-kx-6\), where k is a constant, crosses the x-axis at two points. What is the value of k?

(1) For each of the two points where the graph crosses the x-axis, the x-coordinate is an integer.

(2) The graph crosses the x-axis at (1,0).

Thanks,

Tim

(1) For each of the two points where the graph crosses the x-axis, the x-coordinate is an integer.

If \(y=(x-2)(x+3)=x^2+x-6\), so if the x-intercepts are 2 and -3, then k=-1.

Not sufficient.

(2) The graph crosses the x-axis at (1,0) --> substitute x=1 and y=0, into the equation: \(0=1^2-k-6\) --> k=-5. Sufficient.

Answer: B.