document.write( "Question 116081: If you could explain to me how to solve this problem, I would appreciate it. I need numerical values for a, b, c, and d. I know this involves substitution, I just don't know where to start! Thank you so much. \r
\n" ); document.write( "\n" ); document.write( "2a+3b-4c+6d=6\r
\n" ); document.write( "\n" ); document.write( "7a-5b-c=-7\r
\n" ); document.write( "\n" ); document.write( "13a-9b=6\r
\n" ); document.write( "\n" ); document.write( "d^2-2d=-1 \n" ); document.write( "
Algebra.Com's Answer #84412 by Edwin McCravy(20060)\"\" \"About 
You can put this solution on YOUR website!
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document.write( " 2a + 3b - 4c + 6d =  6 \r\n" );
document.write( " 7a - 5b - c       = -7 \r\n" );
document.write( "13a - 9b           =  6 \r\n" );
document.write( "           dē - 2d = -1\r\n" );
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document.write( "Solve the last equation first, since\r\n" );
document.write( "that is the only equation that has \r\n" );
document.write( "just one unknown:\r\n" );
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document.write( "       dē - 2d = -1\r\n" );
document.write( "   dē - 2d + 1 =  0\r\n" );
document.write( "(d - 1)(d - 1) =  0\r\n" );
document.write( "d - 1 = 0 or d =  1\r\n" );
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document.write( "Substitute d = 1 into the first \r\n" );
document.write( "equation:\r\n" );
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document.write( "  2a + 3b - 4c + 6d = 6\r\n" );
document.write( "2a + 3b - 4c + 6(1) = 6\r\n" );
document.write( "   2a + 3b - 4c + 6 = 6\r\n" );
document.write( "       2a + 3b - 4c = 0\r\n" );
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document.write( "So now the system of equations is:\r\n" );
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document.write( " 2a + 3b - 4c =  0\r\n" );
document.write( " 7a - 5b -  c = -7 \r\n" );
document.write( "13a - 9b      =  6\r\n" );
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document.write( "Can you solve that system? If not,\r\n" );
document.write( "post again asking how.\r\n" );
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document.write( "Answer:  a = 6, b = 8, c = 9 \r\n" );
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document.write( "and earlier we found d = 1.\r\n" );
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document.write( "Edwin
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