document.write( "Question 656152: find if the points joining A(6,7,1), B(2,-3,1) and C(4,-5,1) are collinear. \n" ); document.write( "
Algebra.Com's Answer #409367 by Edwin McCravy(20056)\"\" \"About 
You can put this solution on YOUR website!
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document.write( "We need to find whether the vector AC is a multiple of the vector AB\r\n" );
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document.write( "AC = < 4-6, -5-7, 1-1 > = < -2, -12, 0 > \r\n" );
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document.write( "AB = < 2-6, -3-7, 1-1 > = < -4, -10, 0 >\r\n" );
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document.write( "AC is not a multiple of AB, so A,B, and C are not collinear.\r\n" );
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document.write( "You can also do it by finding the distances between the three points,\r\n" );
document.write( "and determining whether the sum of two of the distances AB, BC, AC are\r\n" );
document.write( "equal to the third distance:\r\n" );
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document.write( "AB = \"sqrt%28+%282-6%29%5E2+%2B+%28-3-7%29%5E2+%2B+%281-1%29%5E2%29\" = \"sqrt%28%28-4%29%5E2%2B%28-10%29%5E2%2B0%5E2%29\" = \"sqrt%2816%2B100%2B0%29\" = \"sqrt%28116%29\" = \"sqrt%284%2A29%29\" = \"2sqrt%2829%29\"\r\n" );
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document.write( "AC = \"sqrt%28+%284-6%29%5E2+%2B+%28-5-7%29%5E2+%2B+%281-1%29%5E2%29\" = \"sqrt%28%28-2%29%5E2%2B%28-12%29%5E2%2B0%5E2%29\" = \"sqrt%284%2B144%2B0%29\" = \"sqrt%28148%29\" = \"sqrt%284%2A37%29\" = \"2sqrt%2837%29\"\r\n" );
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document.write( "BC = \"sqrt%28+%284-2%29%5E2+%2B+%28-5-%28-3%29%29%5E2+%2B+%281-1%29%5E2%29\" = \"sqrt%28%282%29%5E2%2B%28-5%2B3%29%5E2%2B0%5E2%29\" = \"sqrt%284%2B%28-2%29%5E2%2B0%29\" = \"sqrt%284%2B4%29\" = \"sqrt%288%29\" = \"sqrt%284%2A2%29\" = \"2sqrt%282%29\"\r\n" );
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document.write( "No two of those have the sum of the smallest two, \"2sqrt%282%29\" + \"2sqrt%2829%29\" \r\n" );
document.write( "does not equal the largest \"2sqrt%2837%29\", so the three points cannot be\r\n" );
document.write( "collinear. \r\n" );
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document.write( "Edwin
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