Two or more lines are said to be concurrent if they intersect in a single point. Two lines concur if their trilinear coordinates satisfy
(1)
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Three lines concur if their trilinear coordinates satisfy
(2)
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(3)
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(4)
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in which case the point is
(5)
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Three lines
(6)
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(7)
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(8)
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are concurrent if their coefficients satisfy
(9)
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