document.write( "Question 469195: Are all linear equations functions? Is there an instance when a linear equations is not a function? Please explain. \n" ); document.write( "
Algebra.Com's Answer #321909 by Edwin McCravy(20055)\"\" \"About 
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document.write( "The only linear equations that are not functions are equations\r\n" );
document.write( "of vertical lines.  They have equations of the form x = a. \r\n" );
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document.write( "such as x = 4 or x = -6 etc.\r\n" );
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document.write( "All other linear equations are functions.  A vertical line does\r\n" );
document.write( "not pass the vertical line test.  That sounds funny, but it's true.\r\n" );
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document.write( "If you look at a vertical line, such as x=4\r\n" );
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document.write( "That illustrates two different points (4,3) and (4,-5) which gives\r\n" );
document.write( "different outputs y=3 and y=-5 for the same input x=4.  In order to\r\n" );
document.write( "represent a function, a graph cannot contain two different points\r\n" );
document.write( "with the same x-value.\r\n" );
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document.write( "Another way of saying it is \"In order for a graph to represent a\r\n" );
document.write( "function, it must not contain any two points such that one is directly\r\n" );
document.write( "above the other or directly below the other.  (4,3) is directly above\r\n" );
document.write( "(4,-5) and (4,-5) is directly below (4,3).  So the graph cannot\r\n" );
document.write( "represent a function.\r\n" );
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document.write( "Edwin
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