document.write( "Question 82903: My teacher doesn't explain well & I don't understand how to do elimination & substitution problems.
\n" ); document.write( "ex.-3x-1/2y=10
\n" ); document.write( " 5x+1/4y=8
\n" ); document.write( "How do I figure out this problem?
\n" ); document.write( "Thank you so much for your help!\r
\n" ); document.write( "\n" ); document.write( "Chapter 8.4 Algebra 1
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Algebra.Com's Answer #59487 by jim_thompson5910(35256)\"\" \"About 
You can put this solution on YOUR website!
First multiply the top equation by 2 to eliminate the denominator\r
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\n" ); document.write( "\n" ); document.write( "\"2%28-3x-%281%2F2%29y%29=2%2810%29\" Multiply both sides by 2\r
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\n" ); document.write( "\n" ); document.write( "\"-6x-y=20\" Distribute\r
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\n" ); document.write( "\n" ); document.write( "Now multiply the bottom equation by 4 to eliminate the denominator\r
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\n" ); document.write( "\n" ); document.write( "\"4%285x%2B%281%2F4%29y%29=4%288%29\" Multiply both sides by 4\r
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\n" ); document.write( "\n" ); document.write( "\"20x%2By=32\" Distribute\r
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\n" ); document.write( "\n" ); document.write( "So after multiplying we get the system of equations:\r
\n" ); document.write( "\n" ); document.write( "\"-6x-y=20\"
\n" ); document.write( "\"20x%2By=32\"\r
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\n" ); document.write( "\n" ); document.write( "So if you want to solve by elimination you would follow this procedure\r
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Solved by pluggable solver: Solving a System of Linear Equations by Elimination/Addition

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\n" ); document.write( " Lets start with the given system of linear equations
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\n" ); document.write( " \"-6%2Ax-1%2Ay=20\"
\n" ); document.write( " \"20%2Ax%2B1%2Ay=32\"
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\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).
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\n" ); document.write( " So lets eliminate x. In order to do that, we need to have both x coefficients that are equal but have opposite signs (for instance 2 and -2 are equal but have opposite signs). This way they will add to zero.
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\n" ); document.write( " So to make the x coefficients equal but opposite, we need to multiply both x coefficients by some number to get them to an equal number. So if we wanted to get -6 and 20 to some equal number, we could try to get them to the LCM.
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\n" ); document.write( " Since the LCM of -6 and 20 is -60, we need to multiply both sides of the top equation by 10 and multiply both sides of the bottom equation by 3 like this:
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\n" ); document.write( " \"10%2A%28-6%2Ax-1%2Ay%29=%2820%29%2A10\" Multiply the top equation (both sides) by 10
\n" ); document.write( " \"3%2A%2820%2Ax%2B1%2Ay%29=%2832%29%2A3\" Multiply the bottom equation (both sides) by 3
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\n" ); document.write( " So after multiplying we get this:
\n" ); document.write( " \"-60%2Ax-10%2Ay=200\"
\n" ); document.write( " \"60%2Ax%2B3%2Ay=96\"
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\n" ); document.write( " Notice how -60 and 60 add to zero (ie \"-60%2B60=0\")
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\n" ); document.write( " Now add the equations together. In order to add 2 equations, group like terms and combine them
\n" ); document.write( " \"%28-60%2Ax%2B60%2Ax%29-10%2Ay%2B3%2Ay%29=200%2B96\"
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\n" ); document.write( " \"%28-60%2B60%29%2Ax-10%2B3%29y=200%2B96\"
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\n" ); document.write( " \"cross%28-60%2B60%29%2Ax%2B%28-10%2B3%29%2Ay=200%2B96\" Notice the x coefficients add to zero and cancel out. This means we've eliminated x altogether.
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\n" ); document.write( " So after adding and canceling out the x terms we're left with:
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\n" ); document.write( " \"-7%2Ay=296\"
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\n" ); document.write( " \"y=296%2F-7\" Divide both sides by \"-7\" to solve for y
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\n" ); document.write( " \"y=-296%2F7\" Reduce
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\n" ); document.write( " Now plug this answer into the top equation \"-6%2Ax-1%2Ay=20\" to solve for x
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\n" ); document.write( " \"-6%2Ax-1%28-296%2F7%29=20\" Plug in \"y=-296%2F7\"
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\n" ); document.write( " \"-6%2Ax%2B296%2F7=20\" Multiply
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\n" ); document.write( "
\n" ); document.write( " \"-6%2Ax%2B296%2F7=20\" Reduce
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\n" ); document.write( " \"-6%2Ax=20-296%2F7\" Subtract \"296%2F7\" from both sides
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\n" ); document.write( " \"-6%2Ax=140%2F7-296%2F7\" Make 20 into a fraction with a denominator of 7
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\n" ); document.write( " \"-6%2Ax=-156%2F7\" Combine the terms on the right side
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\n" ); document.write( " \"cross%28%281%2F-6%29%28-6%29%29%2Ax=%28-156%2F7%29%281%2F-6%29\" Multiply both sides by \"1%2F-6\". This will cancel out \"-6\" on the left side.
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\n" ); document.write( " \"x=26%2F7\" Multiply the terms on the right side
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\n" ); document.write( " So our answer is
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\n" ); document.write( " \"x=26%2F7\", \"y=-296%2F7\"
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\n" ); document.write( " which also looks like
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\n" ); document.write( " (\"26%2F7\", \"-296%2F7\")
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\n" ); document.write( " Notice if we graph the equations (if you need help with graphing, check out this solver)
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\n" ); document.write( " \"-6%2Ax-1%2Ay=20\"
\n" ); document.write( " \"20%2Ax%2B1%2Ay=32\"
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\n" ); document.write( " we get
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\n" ); document.write( " graph of \"-6%2Ax-1%2Ay=20\" (red) \"20%2Ax%2B1%2Ay=32\" (green) (hint: you may have to solve for y to graph these) and the intersection of the lines (blue circle).
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\n" ); document.write( " and we can see that the two equations intersect at (\"26%2F7\",\"-296%2F7\"). This verifies our answer.

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\n" ); document.write( "\n" ); document.write( "Or if you want to solve by substitution you would follow this procedure\r
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Solved by pluggable solver: Solving a linear system of equations by subsitution

\n" ); document.write( "
\n" ); document.write( " Lets start with the given system of linear equations
\n" ); document.write( "
\n" ); document.write( " \"-6%2Ax-1%2Ay=20\"
\n" ); document.write( " \"20%2Ax%2B1%2Ay=32\"
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\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 choose y.
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\n" ); document.write( " Solve for y for the first equation
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\n" ); document.write( " \"-1%2Ay=20%2B6%2Ax\"Add \"6%2Ax\" to both sides
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\n" ); document.write( " \"y=%2820%2B6%2Ax%29%2F-1\" Divide both sides by -1.
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\n" ); document.write( " Which breaks down and reduces to
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\n" ); document.write( " \"y=-20-6%2Ax\" Now we've fully isolated y
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\n" ); document.write( " Since y equals \"-20-6%2Ax\" we can substitute the expression \"-20-6%2Ax\" into y of the 2nd equation. This will eliminate y so we can solve for x.
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\n" ); document.write( " \"20%2Ax%2B1%2Ahighlight%28%28-20-6%2Ax%29%29=32\" Replace y with \"-20-6%2Ax\". Since this eliminates y, we can now solve for x.
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\n" ); document.write( " \"20%2Ax%2B1%2A%28-20%29%2B1%28-6%29x=32\" Distribute 1 to \"-20-6%2Ax\"
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\n" ); document.write( " \"20%2Ax-20-6%2Ax=32\" Multiply
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\n" ); document.write( " \"20%2Ax-20-6%2Ax=32\" Reduce any fractions
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\n" ); document.write( " \"20%2Ax-6%2Ax=32%2B20\"Add \"20\" to both sides
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\n" ); document.write( " \"20%2Ax-6%2Ax=52\" Combine the terms on the right side
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\n" ); document.write( " \"14%2Ax=52\" Now combine the terms on the left side.
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\n" ); document.write( " \"cross%28%281%2F14%29%2814%2F1%29%29x=%2852%2F1%29%281%2F14%29\" Multiply both sides by \"1%2F14\". This will cancel out \"14%2F1\" and isolate x
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\n" ); document.write( " So when we multiply \"52%2F1\" and \"1%2F14\" (and simplify) we get
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\n" ); document.write( " \"x=26%2F7\" <---------------------------------One answer
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\n" ); document.write( " Now that we know that \"x=26%2F7\", lets substitute that in for x to solve for y
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\n" ); document.write( " \"20%2826%2F7%29%2B1%2Ay=32\" Plug in \"x=26%2F7\" into the 2nd equation
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\n" ); document.write( " \"520%2F7%2B1%2Ay=32\" Multiply
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\n" ); document.write( " \"1%2Ay=32-520%2F7\"Subtract \"520%2F7\" from both sides
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\n" ); document.write( " \"1%2Ay=224%2F7-520%2F7\" Make 32 into a fraction with a denominator of 7
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\n" ); document.write( " \"1%2Ay=-296%2F7\" Combine the terms on the right side
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\n" ); document.write( " \"cross%28%281%2F1%29%281%29%29%2Ay=%28-296%2F7%29%281%2F1%29\" Multiply both sides by \"1%2F1\". This will cancel out 1 on the left side.
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\n" ); document.write( " \"y=-296%2F7\" Multiply the terms on the right side
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\n" ); document.write( "
\n" ); document.write( " \"y=-296%2F7\" Reduce
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\n" ); document.write( " So this is the other answer
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\n" ); document.write( " \"y=-296%2F7\"<---------------------------------Other answer
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\n" ); document.write( " So our solution is
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\n" ); document.write( " \"x=26%2F7\" and \"y=-296%2F7\"
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\n" ); document.write( " which can also look like
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\n" ); document.write( " (\"26%2F7\",\"-296%2F7\")
\n" ); document.write( "
\n" ); document.write( " Notice if we graph the equations (if you need help with graphing, check out this solver)
\n" ); document.write( "
\n" ); document.write( " \"-6%2Ax-1%2Ay=20\"
\n" ); document.write( " \"20%2Ax%2B1%2Ay=32\"
\n" ); document.write( "
\n" ); document.write( " we get
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\n" ); document.write( "
\n" ); document.write( " graph of \"-6%2Ax-1%2Ay=20\" (red) and \"20%2Ax%2B1%2Ay=32\" (green) (hint: you may have to solve for y to graph these) intersecting at the blue circle.
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\n" ); document.write( "
\n" ); document.write( " and we can see that the two equations intersect at (\"26%2F7\",\"-296%2F7\"). This verifies our answer.
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\n" ); document.write( "
\n" ); document.write( " -----------------------------------------------------------------------------------------------
\n" ); document.write( " Check:
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\n" ); document.write( " Plug in (\"26%2F7\",\"-296%2F7\") into the system of equations
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\n" ); document.write( "
\n" ); document.write( " Let \"x=26%2F7\" and \"y=-296%2F7\". Now plug those values into the equation \"-6%2Ax-1%2Ay=20\"
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\n" ); document.write( " \"-6%2A%2826%2F7%29-1%2A%28-296%2F7%29=20\" Plug in \"x=26%2F7\" and \"y=-296%2F7\"
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\n" ); document.write( " \"-156%2F7%2B296%2F7=20\" Multiply
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\n" ); document.write( "
\n" ); document.write( " \"140%2F7=20\" Add
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\n" ); document.write( " \"20=20\" Reduce. Since this equation is true the solution works.
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\n" ); document.write( " So the solution (\"26%2F7\",\"-296%2F7\") satisfies \"-6%2Ax-1%2Ay=20\"
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\n" ); document.write( " Let \"x=26%2F7\" and \"y=-296%2F7\". Now plug those values into the equation \"20%2Ax%2B1%2Ay=32\"
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\n" ); document.write( " \"20%2A%2826%2F7%29%2B1%2A%28-296%2F7%29=32\" Plug in \"x=26%2F7\" and \"y=-296%2F7\"
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\n" ); document.write( "
\n" ); document.write( " \"520%2F7-296%2F7=32\" Multiply
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\n" ); document.write( " \"224%2F7=32\" Add
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\n" ); document.write( " \"32=32\" Reduce. Since this equation is true the solution works.
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\n" ); document.write( " So the solution (\"26%2F7\",\"-296%2F7\") satisfies \"20%2Ax%2B1%2Ay=32\"
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\n" ); document.write( " Since the solution (\"26%2F7\",\"-296%2F7\") satisfies the system of equations
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\n" ); document.write( " \"-6%2Ax-1%2Ay=20\"
\n" ); document.write( " \"20%2Ax%2B1%2Ay=32\"
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\n" ); document.write( "
\n" ); document.write( " this verifies our answer.
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