Update points_lines_vectors.cpp

1 files changed, 1 insertions, 0 deletions

diff --git a/Geometry/points_lines_vectors.cpp b/Geometry/points_lines_vectors.cpp
index 9e9af91..f381ea8 100644
--- a/Geometry/points_lines_vectors.cpp
+++ b/Geometry/points_lines_vectors.cpp
@@ -27,6 +27,7 @@ double angle(point a, point o, point b) {
 	return acos(dot(oa, ob) / sqrt(norm_sq(oa) * norm_sq(ob)));
 }
 
+// (q.x - p.x) * (r.y - p.y) - (r.x - p.x) * (q.y - p.y)
 bool ccw(point p, point q, point r) { return cross(vec(p, q), vec(p, r)) > 0; }
 
 struct line {