RE: Beginner Question

*To*: mathgroup at smc.vnet.net*Subject*: [mg66588] RE: [mg66561] Beginner Question*From*: spiraltooth <spiraltooth at optonline.net>*Date*: Sun, 21 May 2006 00:29:33 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

xA=x(A) xB=x(B) xC=x(c) yA=y(A) yB=y(B) yC=y(C) m=(yA-yB)/(xA-xB) b=yA-(m*xA) If[xC-((yC-b)/m)<0,Left,Right] For example if point A is {1,2} and point B is {2,3} and point C is {3,4}: xA = 1 xB = 2 xC = 3 yA = 2 yB = 3 yC = 4 m = (yA - yB)/(xA - xB) b = yA - (m*xA) If[xC - ((yC - b)/m) < 0, Left, Right] Out[1]= 1 Out[2]= 2 Out[3]= 3 Out[4]= 2 Out[5]= 3 Out[6]= 4 Out[7]= 1 Out[8]= 1 Out[9]= Right Best regards, Alan -----Original Message----- From: akil [mailto:akil39 at gmail.com] To: mathgroup at smc.vnet.net Subject: [mg66588] [mg66561] Beginner Question Hi, Suppose I have three 2D points A, B, C. And two points, namely A and B form a line. How can I determine in mathematica on which side, (so which half-plane formed by) of the line, point C is. So when I input three points I want to know if the third point is on the left or right side of the half plane formed by the line (ray) A,B. Appreciate any help.