http:Q_20377676.html [http:Q_20377676.html]

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actually I can find whether the point lies inside or outside the triangle,but I cannot test the forth point if it lies on the boundary of the triangle.(I am using C program)Also,I am not given the angle.
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actually I can find whether the point lies inside or outside the triangle,but I cannot test the forth point if it lies on the boundary of the triangle.(I am using C program)Also,I am not given the angle.

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the point is on the triangle if it is on one of the line segments.<br />
using the point in polygon test mentioned above, instead of a sign change, you would get 0
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the point is on the triangle if it is on one of the line segments.
using the point in polygon test mentioned above, instead of a sign change, you would get 0

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<a href="http://tog.acm.org/editors/erich/ptinpoly/" rel="ugc">http://tog.acm.org/editors/erich/ptinpoly/</a><br />
<a href="http://en.wikipedia.org/wiki/Point_in_polygon" rel="ugc">http://en.wikipedia.org/wiki/Point_in_polygon</a><br />
<a href="http://local.wasp.uwa.edu.au/~pbourke/geometry/insidepoly/" rel="ugc">http://local.wasp.uwa.edu.au/~pbourke/geometry/insidepoly/</a>
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http://tog.acm.org/editors/erich/ptinpoly/ [http://tog.acm.org/editors/erich/ptinpoly/]
http://en.wikipedia.org/wiki/Point_in_polygon [http://en.wikipedia.org/wiki/Point_in_polygon]
http://local.wasp.uwa.edu.au/~pbourke/geometry/insidepoly/ [http://local.wasp.uwa.edu.au/~pbourke/geometry/insidepoly/]

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<a href="http://mathforum.org/library/drmath/view/54505.html" rel="ugc">http://mathforum.org/library/drmath/view/54505.html</a>
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http://mathforum.org/library/drmath/view/54505.html [http://mathforum.org/library/drmath/view/54505.html]

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To test if a point lies exactly on a line<br />
<a href="http://mathworld.wolfram.com/Collinear.html" rel="ugc">http://mathworld.wolfram.com/Collinear.html</a><br />
To lie on a line segment it would also have to be between the end points.
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To test if a point lies exactly on a line
http://mathworld.wolfram.com/Collinear.html [http://mathworld.wolfram.com/Collinear.html]
To lie on a line segment it would also have to be between the end points.

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It is given that there are four points where three points are used to form a traingle.How can I know the forth point whether it lies on the triangle(not inside or outside the triangle)?Can someone help me with this little problem?Thank you!
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It is given that there are four points where three points are used to form a traingle.How can I know the forth point whether it lies on the triangle(not inside or outside the triangle)?Can someone help me with this little problem?Thank you!

Does a point lie on the triangle?

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