document.write( "Question 639514: 4a + 9b = 8
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Algebra.Com's Answer #402773 by AnlytcPhil(1806)\"\" \"About 
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4a + 9b = 8
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document.write( "Write the system so that the terms of like variables\r\n" );
document.write( "line up vertically like this\r\n" );
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document.write( "4a + 9b       = 8\r\n" );
document.write( "8a      + 6c = -1\r\n" );
document.write( "     6b + 6c = -1\r\n" );
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document.write( "The letter c does not appear in the first equation, thus \r\n" );
document.write( "c is already eliminated from the first equation\r\n" );
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document.write( "So we will eliminate c from the other two equations.\r\n" );
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document.write( "We multiply the 3rd equation by -1 and add it to the\r\n" );
document.write( "2nd equation \r\n" );
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document.write( "8a      + 6c = -1\r\n" );
document.write( "    -6b - 6c =  1\r\n" );
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document.write( "8a - 6b      =  0\r\n" );
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document.write( "That can be divided through by 2\r\n" );
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document.write( "4a - 3b = 0\r\n" );
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document.write( "Now we have a system of 2 equations in 2 unknowns a and b\r\n" );
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document.write( "4a + 9b = 8\r\n" );
document.write( "4a - 3b = 0\r\n" );
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document.write( "Multiplying the bottom equation by -1 and adding to the first\r\n" );
document.write( "equation:\r\n" );
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document.write( " 4a + 9b = 8\r\n" );
document.write( "-4a + 3b = 0\r\n" );
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document.write( "     12b = 8\r\n" );
document.write( "       b = \"8%2F12\"\r\n" );
document.write( "       b = \"2%2F3\"\r\n" );
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document.write( "Substituting that into\r\n" );
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document.write( "4a - 3b = 0\r\n" );
document.write( "4a - 3\"2%2F3\" = 0\r\n" );
document.write( "4a - 2 = 0\r\n" );
document.write( "    4a = 2\r\n" );
document.write( "     a = \"2%2F4\"\r\n" );
document.write( "     a = \"1%2F2\"\r\n" );
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document.write( "Substituting b = \"2%2F3\" into the original\r\n" );
document.write( "3rd equation:\r\n" );
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document.write( "6b + 6c = -1\r\n" );
document.write( "6·\"2%2F3\" + 6c = -1\r\n" );
document.write( " 4 + 6c = -1\r\n" );
document.write( "     6c = -5\r\n" );
document.write( "      c = \"-5%2F6\"\r\n" );
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document.write( "Solution (a, b, c) = (\"1%2F2\",\"2%2F3\",\"-5%2F6\")  \r\n" );
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document.write( "Edwin

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