document.write( "Question 89301: Solve the system by addition. 5x – 3y = 5 x – 5y = 1\r
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\n" ); document.write( "\n" ); document.write( "Solve the system by addition. 3x + 8y = 7 6x – 4y = –1
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Algebra.Com's Answer #64880 by jim_thompson5910(35256)\"\" \"About 
You can put this solution on YOUR website!
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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( " \"5%2Ax-3%2Ay=5\"
\n" ); document.write( " \"1%2Ax-5%2Ay=1\"
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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 5 and 1 to some equal number, we could try to get them to the LCM.
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\n" ); document.write( " Since the LCM of 5 and 1 is 5, we need to multiply both sides of the top equation by 1 and multiply both sides of the bottom equation by -5 like this:
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\n" ); document.write( " \"1%2A%285%2Ax-3%2Ay%29=%285%29%2A1\" Multiply the top equation (both sides) by 1
\n" ); document.write( " \"-5%2A%281%2Ax-5%2Ay%29=%281%29%2A-5\" Multiply the bottom equation (both sides) by -5
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\n" ); document.write( " So after multiplying we get this:
\n" ); document.write( " \"5%2Ax-3%2Ay=5\"
\n" ); document.write( " \"-5%2Ax%2B25%2Ay=-5\"
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\n" ); document.write( " Notice how 5 and -5 add to zero (ie \"5%2B-5=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( " \"%285%2Ax-5%2Ax%29-3%2Ay%2B25%2Ay%29=5-5\"
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\n" ); document.write( " \"%285-5%29%2Ax-3%2B25%29y=5-5\"
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\n" ); document.write( " \"cross%285%2B-5%29%2Ax%2B%28-3%2B25%29%2Ay=5-5\" 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( " \"22%2Ay=0\"
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\n" ); document.write( " \"y=0%2F22\" Divide both sides by \"22\" to solve for y
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\n" ); document.write( " \"y=0\" Reduce
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\n" ); document.write( " Now plug this answer into the top equation \"5%2Ax-3%2Ay=5\" to solve for x
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\n" ); document.write( " \"5%2Ax-3%280%29=5\" Plug in \"y=0\"
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\n" ); document.write( " \"5%2Ax%2B0=5\" Multiply
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\n" ); document.write( " \"5%2Ax=5-0\" Subtract \"0\" from both sides
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\n" ); document.write( " \"5%2Ax=5\" Combine the terms on the right side
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\n" ); document.write( " \"cross%28%281%2F5%29%285%29%29%2Ax=%285%29%281%2F5%29\" Multiply both sides by \"1%2F5\". This will cancel out \"5\" on the left side.
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\n" ); document.write( " \"x=1\" 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=1\", \"y=0\"
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\n" ); document.write( " which also looks like
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\n" ); document.write( " (\"1\", \"0\")
\n" ); document.write( "
\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( " \"5%2Ax-3%2Ay=5\"
\n" ); document.write( " \"1%2Ax-5%2Ay=1\"
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\n" ); document.write( " we get
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\n" ); document.write( " graph of \"5%2Ax-3%2Ay=5\" (red) \"1%2Ax-5%2Ay=1\" (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 (\"1\",\"0\"). This verifies our answer.

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Solved by pluggable solver: Solving a System of Linear Equations by Elimination/Addition

\n" ); document.write( "
\n" ); document.write( " Lets start with the given system of linear equations
\n" ); document.write( "
\n" ); document.write( " \"3%2Ax%2B8%2Ay=7\"
\n" ); document.write( " \"6%2Ax-4%2Ay=-1\"
\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).
\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 but have opposite signs (for instance 2 and -2 are equal but have opposite signs). This way they will add to zero.
\n" ); document.write( "
\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 3 and 6 to some equal number, we could try to get them to the LCM.
\n" ); document.write( "
\n" ); document.write( " Since the LCM of 3 and 6 is 6, we need to multiply both sides of the top equation by 2 and multiply both sides of the bottom equation by -1 like this:
\n" ); document.write( "
\n" ); document.write( " \"2%2A%283%2Ax%2B8%2Ay%29=%287%29%2A2\" Multiply the top equation (both sides) by 2
\n" ); document.write( " \"-1%2A%286%2Ax-4%2Ay%29=%28-1%29%2A-1\" Multiply the bottom equation (both sides) by -1
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\n" ); document.write( "
\n" ); document.write( " So after multiplying we get this:
\n" ); document.write( " \"6%2Ax%2B16%2Ay=14\"
\n" ); document.write( " \"-6%2Ax%2B4%2Ay=1\"
\n" ); document.write( "
\n" ); document.write( " Notice how 6 and -6 add to zero (ie \"6%2B-6=0\")
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " Now add the equations together. In order to add 2 equations, group like terms and combine them
\n" ); document.write( " \"%286%2Ax-6%2Ax%29%2B%2816%2Ay%2B4%2Ay%29=14%2B1\"
\n" ); document.write( "
\n" ); document.write( " \"%286-6%29%2Ax%2B%2816%2B4%29y=14%2B1\"
\n" ); document.write( "
\n" ); document.write( " \"cross%286%2B-6%29%2Ax%2B%2816%2B4%29%2Ay=14%2B1\" Notice the x coefficients add to zero and cancel out. This means we've eliminated x altogether.
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\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " So after adding and canceling out the x terms we're left with:
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\n" ); document.write( " \"20%2Ay=15\"
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\n" ); document.write( " \"y=15%2F20\" Divide both sides by \"20\" to solve for y
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\n" ); document.write( " \"y=3%2F4\" Reduce
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\n" ); document.write( " Now plug this answer into the top equation \"3%2Ax%2B8%2Ay=7\" to solve for x
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\n" ); document.write( " \"3%2Ax%2B8%283%2F4%29=7\" Plug in \"y=3%2F4\"
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\n" ); document.write( " \"3%2Ax%2B24%2F4=7\" Multiply
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\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"3%2Ax%2B6=7\" Reduce
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\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"3%2Ax=7-6\" Subtract \"6\" from both sides
\n" ); document.write( "
\n" ); document.write( " \"3%2Ax=1\" Combine the terms on the right side
\n" ); document.write( "
\n" ); document.write( " \"cross%28%281%2F3%29%283%29%29%2Ax=%281%29%281%2F3%29\" Multiply both sides by \"1%2F3\". This will cancel out \"3\" on the left side.
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\n" ); document.write( " \"x=1%2F3\" Multiply the terms on the right side
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\n" ); document.write( "
\n" ); document.write( " So our answer is
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\n" ); document.write( " \"x=1%2F3\", \"y=3%2F4\"
\n" ); document.write( "
\n" ); document.write( " which also looks like
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\n" ); document.write( " (\"1%2F3\", \"3%2F4\")
\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( " \"3%2Ax%2B8%2Ay=7\"
\n" ); document.write( " \"6%2Ax-4%2Ay=-1\"
\n" ); document.write( "
\n" ); document.write( " we get
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " graph of \"3%2Ax%2B8%2Ay=7\" (red) \"6%2Ax-4%2Ay=-1\" (green) (hint: you may have to solve for y to graph these) and the intersection of the lines (blue circle).
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " and we can see that the two equations intersect at (\"1%2F3\",\"3%2F4\"). This verifies our answer.
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