document.write( "Question 971051: The number of straight lines that can be formed by joining 10 points no three of which are in the same straight line except 7 of them which are in the same straight line, is \n" ); document.write( "

Algebra.Com's Answer #593636 by Edwin McCravy(20055) $\"\"$ $\"About$

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The number of straight lines that can be formed by joining 10 points no three of
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document.write( "Suppose the 7 points points A through G are in the same straight line.\r\n" );
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document.write( "That's 1 straight line.\r\n" );
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document.write( "Suppose H, I, J, are not, and that no three other than A through G are \r\n" );
document.write( "in a straight line.\r\n" );
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document.write( "We can connect the 3 points that aren't in a straight line three\r\n" );
document.write( "ways, HI, HJ, and IJ.\r\n" );
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document.write( "That's 3 more straight lines.\r\n" );
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document.write( "We can connect H and each of the 7 points A through G\r\n" );
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document.write( "That's 7 more straight lines\r\n" );
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document.write( "We can connect I and each of the 7 points A through G\r\n" );
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document.write( "That's 7 more straight lines \r\n" );
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document.write( "We can connect J and each of the 7 points A through G\r\n" );
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document.write( "That's 7 more straight lines.\r\n" );
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document.write( "Total 1+3+7+7+7 = 25 lines\r\n" );
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document.write( "Edwin

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