document.write( "Question 642929: Write an equation of the direct variation that includes the point (9,-12). \n" ); document.write( "
Algebra.Com's Answer #404281 by Edwin McCravy(20056)\"\" \"About 
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document.write( "Every equation of direct variation is of the form\r\n" );
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document.write( "      y = k·x\r\n" );
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document.write( "where y and x can be any variable and k is a constant number.\r\n" );
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document.write( "Since it must include the point (9,-12) we know that if we\r\n" );
document.write( "substitute x=9 and y=-12 into y = kx we will have a true\r\n" );
document.write( "equation, so we do that:\r\n" );
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document.write( "      y = k·x\r\n" );
document.write( "    -12 = k·9\r\n" );
document.write( "    -12 = 9k\r\n" );
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document.write( "We divide both sides by 9 to solve for k:\r\n" );
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document.write( "    \"%28-12%29%2F9\" = \"9k%2F9\"\r\n" );
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document.write( "    \"-4%2F3\" = k\r\n" );
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document.write( "So the constant k is \"-4%2F3\", and so we substitute that for k in\r\n" );
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document.write( "      y = k·x\r\n" );
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document.write( "and get the answer:\r\n" );
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document.write( "      y = \"-4%2F3\"x\r\n" );
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document.write( "Edwin
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