document.write( "Question 684140: Solve the following system of equations for the unknown variables. a + b = 7
\n" ); document.write( ",a + c = 12,b + c = 15 \n" ); document.write( "
Algebra.Com's Answer #423929 by ankor@dixie-net.com(22740)\"\" \"About 
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a + b = 7,
\n" ); document.write( " a + c = 12,
\n" ); document.write( " b + c = 15
\n" ); document.write( ":
\n" ); document.write( "a + c = 12
\n" ); document.write( "a = (12-c)
\n" ); document.write( "and
\n" ); document.write( "b + c = 15
\n" ); document.write( "b = (15-c)
\n" ); document.write( ":
\n" ); document.write( "The 1st equation
\n" ); document.write( "a + b = 7
\n" ); document.write( "Replace a and b
\n" ); document.write( "(12-c) + (15-c) = 7
\n" ); document.write( "-2c + 27 = 7
\n" ); document.write( "-2c = 7 - 27
\n" ); document.write( "-2c = - 20
\n" ); document.write( "c = +10
\n" ); document.write( "then
\n" ); document.write( "a + 10 = 12
\n" ); document.write( "a = 2
\n" ); document.write( "and
\n" ); document.write( "b + 10 = 15
\n" ); document.write( "b = 5
\n" ); document.write( ":
\n" ); document.write( "You can check these solution in the original equations
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