Point in Triangle
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To determine whether a point is in a triangle, draw a ray out from the point. If it crosses the boundary of the triangle once, then the point is inside the triangle. If the ray crosses zero or two times, the point is outside. In this example you can drag the point and the Demonstration determines (and counts) the intersection points. This technique can be generalized to an arbitrary nonconvex polygon.
Contributed by: Michael John Twardos (March 2011)
Additional contributions by: Eric W. Weisstein
Open content licensed under CC BY-NC-SA
"Point in Triangle"
Wolfram Demonstrations Project
Published: March 7 2011