document.write( "Question 173267: I am having a problem understanding how to solve a system byusing substitution.
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\n" ); document.write( "1. y = -3x+19
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\n" ); document.write( "\n" ); document.write( "2. y = x +4
\n" ); document.write( " 3x-2y=6\r
\n" ); document.write( "\n" ); document.write( "3. 2x-y = 4
\n" ); document.write( " 2x-y=3\r
\n" ); document.write( "\n" ); document.write( "I've looked at tons of reasons on how these problems work, and none of them make sense. The ones I've looked at are not specific enough on the what, why and how of the problem.
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\n" ); document.write( "Angela
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Algebra.Com's Answer #128087 by jim_thompson5910(35256)\"\" \"About 
You can put this solution on YOUR website!
The goal of solving ANY system of equations with 2 variables is to eliminate one variable so you can solve for the other variable. To eliminate one variable, simply \"substitute\" an expression in terms of the other variable. \r
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\n" ); document.write( "\n" ); document.write( "Note: I'm assuming that the second equation is \"y+=+2x-1\"\r
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\n" ); document.write( "\n" ); document.write( "\"y+=+-3x%2B19\" Start with the first equation\r
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\n" ); document.write( "\n" ); document.write( "\"2x-1+=+-3x%2B19\" Plug in \"y+=+2x-1\". In other words, replace \"y\" with 2x-1. Notice how the \"y\" term is gone.\r
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\n" ); document.write( "\n" ); document.write( "Now we can solve for \"x\".\r
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\n" ); document.write( "\n" ); document.write( "\"2x=-3x%2B19%2B1\" Add \"1\" to both sides.\r
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\n" ); document.write( "\n" ); document.write( "\"2x%2B3x=19%2B1\" Add \"3x\" to both sides.\r
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\n" ); document.write( "\n" ); document.write( "\"5x=19%2B1\" Combine like terms on the left side.\r
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\n" ); document.write( "\n" ); document.write( "\"5x=20\" Combine like terms on the right side.\r
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\n" ); document.write( "\n" ); document.write( "\"x=%2820%29%2F%285%29\" Divide both sides by \"5\" to isolate \"x\".\r
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\n" ); document.write( "\n" ); document.write( "\"x=4\" Reduce. So this is the first answer.\r
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\n" ); document.write( "\n" ); document.write( "\"y+=+2x-1\" Go back to the second equation\r
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\n" ); document.write( "\n" ); document.write( "\"y+=+2%284%29-1\" Plug in \"x=4\"\r
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\n" ); document.write( "\n" ); document.write( "\"y+=+8-1\" Multiply\r
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\n" ); document.write( "\n" ); document.write( "\"y+=+7\" Subtract. So this is the second answer.\r
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\n" ); document.write( "\n" ); document.write( "So the solutions are \"x=4\" and \"y+=+7\"\r
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\n" ); document.write( "\n" ); document.write( "which form the ordered pair (4,7)\r
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\n" ); document.write( "\n" ); document.write( "So the system is consistent and independent.\r
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\n" ); document.write( "\n" ); document.write( "# 2\r
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\n" ); document.write( "\n" ); document.write( "\"3x-2y=6+\" Start with the second equation\r
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\n" ); document.write( "\n" ); document.write( "\"3x-2%28x%2B4%29=6+\" Plug in \"y+=+x+%2B4\". In other words, replace \"y\" with x+4. Notice how the \"y\" term is gone.\r
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\n" ); document.write( "\n" ); document.write( "Now we can solve for \"x\".\r
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\n" ); document.write( "\n" ); document.write( "\"3x-2x-8=6\" Distribute.\r
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\n" ); document.write( "\n" ); document.write( "\"x-8=6\" Combine like terms on the left side.\r
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\n" ); document.write( "\n" ); document.write( "\"x=6%2B8\" Add \"8\" to both sides.\r
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\n" ); document.write( "\n" ); document.write( "\"x=14\" Combine like terms on the right side. So this is the first answer.\r
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\n" ); document.write( "\n" ); document.write( "\"y+=+x+%2B4\" Go back to the first equation\r
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\n" ); document.write( "\n" ); document.write( "\"y+=+14+%2B4\" Plug in \"x=14\"\r
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\n" ); document.write( "\n" ); document.write( "\"y+=+18\" Add. So this is the second answer.\r
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\n" ); document.write( "\n" ); document.write( "So the solutions are \"x=14\" and \"y+=+18\"\r
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\n" ); document.write( "\n" ); document.write( "which form the ordered pair (14,18)\r
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\n" ); document.write( "\n" ); document.write( "So the system is consistent and independent.\r
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\n" ); document.write( "\n" ); document.write( "# 3\r
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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%282x-y=4%2C2x-y=3%29\"\r
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\n" ); document.write( "\n" ); document.write( "Now in order to solve this system by using substitution, 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( "So let's isolate y in the first equation\r
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\n" ); document.write( "\n" ); document.write( "\"2x-y=4\" Start with the first equation\r
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\n" ); document.write( "\n" ); document.write( "\"-y=4-2x\" Subtract \"2x\" from both sides\r
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\n" ); document.write( "\n" ); document.write( "\"-y=-2x%2B4\" Rearrange the equation\r
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\n" ); document.write( "\n" ); document.write( "\"y=%28-2x%2B4%29%2F%28-1%29\" Divide both sides by \"-1\"\r
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\n" ); document.write( "\n" ); document.write( "\"y=%28%28-2%29%2F%28-1%29%29x%2B%284%29%2F%28-1%29\" Break up the fraction\r
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\n" ); document.write( "\n" ); document.write( "\"y=2x-4\" Reduce\r
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\n" ); document.write( "\n" ); document.write( "Since \"y=2x-4\", we can now replace each \"y\" in the second equation with \"2x-4\" to solve for \"x\"\r
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\n" ); document.write( "\n" ); document.write( "\"2x-highlight%28%282x-4%29%29=3\" Plug in \"y=2x-4\" into the second equation. In other words, replace each \"y\" with \"2x-4\". Notice we've eliminated the \"y\" variables. So we now have a simple equation with one unknown.\r
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\n" ); document.write( "\n" ); document.write( "\"2x-2x%2B4=3\" Distribute the negative\r
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\n" ); document.write( "\n" ); document.write( "\"4=3\" Combine like terms on the left side\r
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\n" ); document.write( "\n" ); document.write( "Since this equation is NEVER true for any x value, this means there are no solutions.\r
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\n" ); document.write( "\n" ); document.write( "So the system is inconsistent.
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