document.write( "Question 1143913: Four lines on the plane have at most N common points. Find N.
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Algebra.Com's Answer #764858 by math_helper(2461) $\"\"$ $\"About$

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document.write( "Think about it ... imagine drawing the lines one at a time:\r
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document.write( "The first line has no lines to cross.  Common points = 0.\r
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document.write( "The 2nd line can cross the first line (at most) once.  Common points = 1.\r
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document.write( "The 3rd line can cross each of the first two lines once.  That's two more.  Common point count is now 1+2 = 3.\r
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document.write( "The 4th line can cross each of the first three lines once.  That's three more. Common point count is now 3+3 = 6.\r
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document.write( "B) 6 \n" );
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