document.write( "Question 133430: Solve the system of equations using the addition (elimination) method.
\n" ); document.write( "If the answer is a unique solution, present it as an ordered pair: (x, y). If not, specify whether the answer is “no solution” or “infinitely many solutions.”
\n" ); document.write( "3x – 2y = -7
\n" ); document.write( "-9x + 6y = 21
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Algebra.Com's Answer #97609 by jim_thompson5910(35256)\"\" \"About 
You can put this solution on YOUR website!
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\n" ); document.write( "\n" ); document.write( "Start with the given system of equations:\r
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\n" ); document.write( "\n" ); document.write( "\"system%283x-2y=-7%2C-9x%2B6y=21%29\"\r
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\n" ); document.write( "\n" ); document.write( "Now in order to solve this system by using elimination/addition, we need to solve (or isolate) one variable. I'm going to solve for y.\r
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\n" ); document.write( "\n" ); document.write( "In order to solve for one variable, we must eliminate the other variable. So if we wanted to solve for \"y\", we would have to eliminate \"x\" (or vice versa).\r
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\n" ); document.write( "\n" ); document.write( "So lets eliminate \"x\". In order to do that, we need to have both \"x\" coefficients that are equal in magnitude but have opposite signs (for instance 2 and -2 are equal in magnitude but have opposite signs). This way they will add to zero. By adding to zero, they can be eliminated.\r
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\n" ); document.write( "\n" ); document.write( "So to make the \"x\" coefficients equal in magnitude but opposite in sign, we need to multiply both \"x\" coefficients by some number to get them to an common number. So if we wanted to get \"3\" and \"-9\" to some equal number, we could try to get them to the LCM.\r
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\n" ); document.write( "\n" ); document.write( "Since the LCM of \"3\" and \"-9\" is \"9\", we need to multiply both sides of the top equation by \"3\" and multiply both sides of the bottom equation by \"1\" like this:\r
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\n" ); document.write( "\n" ); document.write( "\"3%283x-2y%29=3%28-7%29\" Multiply the top equation (both sides) by \"3\"
\n" ); document.write( "\"1%28-9x%2B6y%29=1%2821%29\" Multiply the bottom equation (both sides) by \"1\"\r
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\n" ); document.write( "\n" ); document.write( "Distribute and multiply\r
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\n" ); document.write( "\n" ); document.write( "\"9x-6y=-21\"
\n" ); document.write( "\"-9x%2B6y=21\"\r
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\n" ); document.write( "\n" ); document.write( "Now add the equations together. In order to add 2 equations, group like terms and combine them\r
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\n" ); document.write( "\n" ); document.write( "\"%289x-9x%29%2B%28-6y%2B6y%29=-21%2B21\"\r
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\n" ); document.write( "\n" ); document.write( "Combine like terms and simplify\r
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\n" ); document.write( "\n" ); document.write( "\"cross%289x-9x%29%2B0y=0\" Notice how the x terms cancel out\r
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\n" ); document.write( "\n" ); document.write( "\"0=0\" Simplify\r
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\n" ); document.write( "\n" ); document.write( "Since this equation is always true regardless of what x or y is, we have an infinite number of solutions. So this system is dependent.
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