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document.write( "Rules for solving a system of three equations in three unknowns:\r\n" );
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document.write( "1. If one of the equations has only two unknowns, call it \"equation 1\".\r\n" );
document.write( "Observe which of the three unknowns is missing from that equation and \r\n" );
document.write( "eliminate that unknown from the other two equations, and call the \r\n" );
document.write( "resulting equation \"equation 2\".\r\n" );
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document.write( "2. If all three equations contain all three unknowns, pick two of the \r\n" );
document.write( "three equations and eliminate an unknown from them, and call the \r\n" );
document.write( "resulting equation \"equation 1\". Us the equation you haven't yet used with \r\n" );
document.write( "one of the others and eliminate that same letter. Call the resulting \r\n" );
document.write( "equation \"equation 2\".\r\n" );
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document.write( "3. Solve the system of two equation in two unknowns, consisting of \"equation\r\n" );
document.write( "1\" and \"equation 2\".\r\n" );
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document.write( "4. Find the third unknown by substituting in one of the original equations \r\n" );
document.write( "that contains that third unknown.\r\n" );
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document.write( "None of the equations have only two unknowns, so step 1 is out. So we go \r\n" );
document.write( "to step 2.\r\n" );
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document.write( "I'll pick the first two equations and eliminate z, since all I have to is \r\n" );
document.write( "add them term by term and the z's will cancel:\r\n" );
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document.write( "Result:\r\n" );
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, that's equation 1.\r\n" );
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document.write( "Now I'll pick the second one and the third one and eliminate that same \r\n" );
document.write( "variable z. All I have to do is add them term by term and the z's will \r\n" );
document.write( "cancel:\r\n" );
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document.write( " Result:\r\n" );
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document.write( "
, that's equation 2.\r\n" );
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document.write( "Step 3 is to solve equation 1 and equation 2:\r\n" );
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\r\n" );
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document.write( " All I have to do is add them term by term and the y's will\r\n" );
document.write( "cancel:\r\n" );
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document.write( "The result is:\r\n" );
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document.write( "Substitute in\r\n" );
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document.write( "Step 4 is to substitute theose two values in one of the original \r\n" );
document.write( "equations to find the third letter z. I'll pick the first original \r\n" );
document.write( "equation:\r\n" );
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document.write( "solution 
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document.write( "Edwin
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document.write( "![\"\"](\"/images/stars/stars-13.gif\")
