## Quarter Wit, Quarter Wisdom: Questions on Intercepts and Vertices

*Posted on on September 6, 2011*

Continuing on our quest to master coordinate geometry, let’s look at a couple of Data Sufficiency questions today. The first question uses a great little concept. The second question has a very important takeaway that we all know but hardly ever implement.

Question 1: In the xy-coordinate plane, line l and line k intersect at the point (5, 4). Is the product of their slopes negative?

1) The product of the x-intercepts of lines l and k is positive.

2) The product of the y-intercepts of lines l and k is negative.