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