document.write( "Question 655658: Write a linear function where f(2)=4,f(4)=2 and f(3)=3. \n" ); document.write( "
Algebra.Com's Answer #409227 by MathLover1(20850)\"\" \"About 
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If \"f%282%29=4\",\"f%284%29=2\", \"f%283%29=3\", then the graph of the function contains the point (\"2\",\"4\"),(\"4\",\"2\"), and (\"3\",\"3\"). \r
\n" ); document.write( "\n" ); document.write( "Use the two point form of an equation of a straight line and the points (\"2\",\"4\"),(\"4\",\"2\"): \r
\n" ); document.write( "\n" ); document.write( "\"f%28x%29-y1=%28%28y1-y2%29%2F%28x1-x2%29%29%28x-x1%29\" where (x1,y1)and (x2,y2) are the coordinates of the given points. \r
\n" ); document.write( "\n" ); document.write( "\"f%28x%29-4=%28%284-2%29%2F%282-4%29%29%28x-2%29\"\r
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\n" ); document.write( "\n" ); document.write( "\"f%28x%29-4=%282%2F-2%29%28x-2%29\"\r
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\n" ); document.write( "\n" ); document.write( "\"f%28x%29-4=-1%28x-2%29\"\r
\n" ); document.write( "\n" ); document.write( "\"f%28x%29-4=-x%2B2\"\r
\n" ); document.write( "\n" ); document.write( "\"f%28x%29=-x%2B2%2B4\"\r
\n" ); document.write( "\n" ); document.write( "\"highlight%28f%28x%29=-x%2B6%29\"\r
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\n" ); document.write( "\n" ); document.write( "\"+graph%28+600%2C+600%2C+-10%2C+10%2C+-10%2C+10%2C+-x%2B6%29+\"\r
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\n" ); document.write( "\n" ); document.write( "here is a proof that all three of given points lie on this line\r
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Solved by pluggable solver: To determine if 3 points lie in a line
The 3 points lie on a same plane. For all points to lie on a line they should satisfy the equation of a line. Hence any two points taken on a line should calculate to the same slope of a line.
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\n" ); document.write( " In order to prove the 3 points to lie on a line, as there exists a unique line containing three points and every line has a unique slope.
\n" ); document.write( " Hence it will be sufficient to prove that the slope calculated taking 2 points at a time should be equal.
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\n" ); document.write( " Slope of line taking points (X1,Y1) and (X2,Y2) is
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\n" ); document.write( " \"slope+=+%28Y2-Y1%29%2F%28X2-X1%29\"
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\n" ); document.write( " \"slope+=+%28%282-4%29%2F%284-2%29%29+=+-1\" ........................(1)
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\n" ); document.write( " Slope of line taking points (X3,Y3) and (X1,Y1) is
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\n" ); document.write( " \"slope+=+%28Y3-Y1%29%2F%28X3-X1%29\"
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\n" ); document.write( " \"slope+=+%28%283-4%29%2F%283-2%29%29+=+-1\" ........................(2)
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\n" ); document.write( " From conditions (1) and (2)
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\n" ); document.write( " The slopes are equal hence the 3 points can lie on same line.
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\n" ); document.write( " If the slope calculated from points (X2,Y2) and (X3,Y3) comes out to be same then it is confirmed that the 3 points lie on a same line.
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\n" ); document.write( " \"slope+=+%28Y3-Y2%29%2F%28X3-X2%29\"
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\n" ); document.write( " \"slope+=+%28%283-2%29%2F%283-4%29%29+=+-1\" ........................(3)
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\n" ); document.write( " From (1),(2) and (3)
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\n" ); document.write( " Hence, It is proved that the 3 points lie on same line.
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\n" ); document.write( " To read more on equations of a line refer to articles on wikipedia
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