Skip to main content
OlympiadHQ

Browse · MATH

Print

jmc

algebra intermediate

Problem

If the three lines , and are drawn in the plane, how many points will lie at the intersection of at least two of the three lines?
Solution
In general, two lines intersect in exactly one point, unless they are parallel, in which case they are either the same line or have no intersection points. First, check to see if any of these lines are parallel. The first line has a slope of , the second line has a slope of , and the third line has a slope of . So, the first and third lines are parallel. We can easily check that these are not the same line. Therefore, these two lines do not intersect anywhere, and the third line intersects each of them in exactly one point, for a total of intersection points.
Final answer
2