document.write( "Question 118519: 3x-4y=5
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Algebra.Com's Answer #86664 by jim_thompson5910(35256)\"\" \"About 
You can put this solution on YOUR website!
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Solved by pluggable solver: Solving a linear system of equations by subsitution

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\n" ); document.write( " Lets start with the given system of linear equations
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\n" ); document.write( " \"3%2Ax-4%2Ay=5\"
\n" ); document.write( " \"-4%2Ax%2B2%2Ay=6\"
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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( " \"-4%2Ay=5-3%2Ax\"Subtract \"3%2Ax\" from both sides
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\n" ); document.write( " \"y=%285-3%2Ax%29%2F-4\" Divide both sides by -4.
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\n" ); document.write( " Which breaks down and reduces to
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\n" ); document.write( " \"y=-5%2F4%2B%283%2F4%29%2Ax\" Now we've fully isolated y
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\n" ); document.write( " Since y equals \"-5%2F4%2B%283%2F4%29%2Ax\" we can substitute the expression \"-5%2F4%2B%283%2F4%29%2Ax\" into y of the 2nd equation. This will eliminate y so we can solve for x.
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\n" ); document.write( " \"-4%2Ax%2B2%2Ahighlight%28%28-5%2F4%2B%283%2F4%29%2Ax%29%29=6\" Replace y with \"-5%2F4%2B%283%2F4%29%2Ax\". Since this eliminates y, we can now solve for x.
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\n" ); document.write( " \"-4%2Ax%2B2%2A%28-5%2F4%29%2B2%283%2F4%29x=6\" Distribute 2 to \"-5%2F4%2B%283%2F4%29%2Ax\"
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\n" ); document.write( " \"-4%2Ax-10%2F4%2B%286%2F4%29%2Ax=6\" Multiply
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\n" ); document.write( " \"-4%2Ax-5%2F2%2B%283%2F2%29%2Ax=6\" Reduce any fractions
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\n" ); document.write( " \"-4%2Ax%2B%283%2F2%29%2Ax=6%2B5%2F2\"Add \"5%2F2\" to both sides
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\n" ); document.write( " \"-4%2Ax%2B%283%2F2%29%2Ax=12%2F2%2B5%2F2\" Make 6 into a fraction with a denominator of 2
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\n" ); document.write( " \"-4%2Ax%2B%283%2F2%29%2Ax=17%2F2\" Combine the terms on the right side
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\n" ); document.write( " \"%28-8%2F2%29%2Ax%2B%283%2F2%29x=17%2F2\" Make -4 into a fraction with a denominator of 2
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\n" ); document.write( " \"%28-5%2F2%29%2Ax=17%2F2\" Now combine the terms on the left side.
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\n" ); document.write( " \"cross%28%282%2F-5%29%28-5%2F2%29%29x=%2817%2F2%29%282%2F-5%29\" Multiply both sides by \"2%2F-5\". This will cancel out \"-5%2F2\" and isolate x
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\n" ); document.write( " So when we multiply \"17%2F2\" and \"2%2F-5\" (and simplify) we get
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\n" ); document.write( " \"x=-17%2F5\" <---------------------------------One answer
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\n" ); document.write( " Now that we know that \"x=-17%2F5\", lets substitute that in for x to solve for y
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\n" ); document.write( " \"-4%28-17%2F5%29%2B2%2Ay=6\" Plug in \"x=-17%2F5\" into the 2nd equation
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\n" ); document.write( " \"68%2F5%2B2%2Ay=6\" Multiply
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\n" ); document.write( " \"2%2Ay=6-68%2F5\"Subtract \"68%2F5\" from both sides
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\n" ); document.write( " \"2%2Ay=30%2F5-68%2F5\" Make 6 into a fraction with a denominator of 5
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\n" ); document.write( " \"2%2Ay=-38%2F5\" Combine the terms on the right side
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\n" ); document.write( " \"cross%28%281%2F2%29%282%29%29%2Ay=%28-38%2F5%29%281%2F2%29\" Multiply both sides by \"1%2F2\". This will cancel out 2 on the left side.
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\n" ); document.write( " \"y=-38%2F10\" Multiply the terms on the right side
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\n" ); document.write( " \"y=-19%2F5\" Reduce
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\n" ); document.write( " So this is the other answer
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\n" ); document.write( " \"y=-19%2F5\"<---------------------------------Other answer
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\n" ); document.write( " So our solution is
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\n" ); document.write( " \"x=-17%2F5\" and \"y=-19%2F5\"
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\n" ); document.write( " which can also look like
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\n" ); document.write( " (\"-17%2F5\",\"-19%2F5\")
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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( " \"3%2Ax-4%2Ay=5\"
\n" ); document.write( " \"-4%2Ax%2B2%2Ay=6\"
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\n" ); document.write( " we get
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\n" ); document.write( " graph of \"3%2Ax-4%2Ay=5\" (red) and \"-4%2Ax%2B2%2Ay=6\" (green) (hint: you may have to solve for y to graph these) intersecting at the blue circle.
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\n" ); document.write( " and we can see that the two equations intersect at (\"-17%2F5\",\"-19%2F5\"). This verifies our answer.
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\n" ); document.write( " Check:
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\n" ); document.write( " Plug in (\"-17%2F5\",\"-19%2F5\") into the system of equations
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\n" ); document.write( " Let \"x=-17%2F5\" and \"y=-19%2F5\". Now plug those values into the equation \"3%2Ax-4%2Ay=5\"
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\n" ); document.write( " \"3%2A%28-17%2F5%29-4%2A%28-19%2F5%29=5\" Plug in \"x=-17%2F5\" and \"y=-19%2F5\"
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\n" ); document.write( " \"-51%2F5%2B76%2F5=5\" Multiply
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\n" ); document.write( " \"25%2F5=5\" Add
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\n" ); document.write( " \"5=5\" Reduce. Since this equation is true the solution works.
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\n" ); document.write( " So the solution (\"-17%2F5\",\"-19%2F5\") satisfies \"3%2Ax-4%2Ay=5\"
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\n" ); document.write( " Let \"x=-17%2F5\" and \"y=-19%2F5\". Now plug those values into the equation \"-4%2Ax%2B2%2Ay=6\"
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\n" ); document.write( " \"-4%2A%28-17%2F5%29%2B2%2A%28-19%2F5%29=6\" Plug in \"x=-17%2F5\" and \"y=-19%2F5\"
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\n" ); document.write( " \"68%2F5-38%2F5=6\" Multiply
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\n" ); document.write( " \"30%2F5=6\" Add
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\n" ); document.write( " \"6=6\" Reduce. Since this equation is true the solution works.
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\n" ); document.write( " So the solution (\"-17%2F5\",\"-19%2F5\") satisfies \"-4%2Ax%2B2%2Ay=6\"
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\n" ); document.write( " Since the solution (\"-17%2F5\",\"-19%2F5\") satisfies the system of equations
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\n" ); document.write( " \"3%2Ax-4%2Ay=5\"
\n" ); document.write( " \"-4%2Ax%2B2%2Ay=6\"
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\n" ); document.write( " this verifies our answer.
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