document.write( "Question 106702: How would you solve this equation, by either using the substitution method or the elimination method?\r
\n" ); document.write( "\n" ); document.write( "3x/4-y/3=7/6\r
\n" ); document.write( "\n" ); document.write( "x/2+2y/3=5/3
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Algebra.Com's Answer #77650 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( " \"%283%2F4%29%2Ax%2B%28-1%2F3%29%2Ay=7%2F6\" Start with the first equation
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\n" ); document.write( " \"12%28%283%2F4%29%2Ax%2B%28-1%2F3%29%2Ay%29=%2812%29%2A%287%2F6%29\" Multiply both sides by the LCD 12
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\n" ); document.write( " \"9%2Ax%2B-4%2Ay=14\"Distribute and simplify
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\n" ); document.write( " \"%281%2F2%29%2Ax%2B%282%2F3%29%2Ay=5%2F3\" Start with the second equation
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\n" ); document.write( " \"6%28%281%2F2%29%2Ax%2B%282%2F3%29%2Ay%29=%286%29%2A%285%2F3%29\" Multiply both sides by the LCD 6
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\n" ); document.write( " \"3%2Ax%2B4%2Ay=10\" Distribute and simplify
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\n" ); document.write( " Lets start with the given system of linear equations
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\n" ); document.write( " \"9%2Ax-4%2Ay=14\"
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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=14-9%2Ax\"Subtract \"9%2Ax\" from both sides
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\n" ); document.write( " \"y=%2814-9%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=-7%2F2%2B%289%2F4%29%2Ax\" Now we've fully isolated y
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\n" ); document.write( " Since y equals \"-7%2F2%2B%289%2F4%29%2Ax\" we can substitute the expression \"-7%2F2%2B%289%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( " \"3%2Ax%2B4%2Ahighlight%28%28-7%2F2%2B%289%2F4%29%2Ax%29%29=10\" Replace y with \"-7%2F2%2B%289%2F4%29%2Ax\". Since this eliminates y, we can now solve for x.
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\n" ); document.write( " \"3%2Ax%2B4%2A%28-7%2F2%29%2B4%289%2F4%29x=10\" Distribute 4 to \"-7%2F2%2B%289%2F4%29%2Ax\"
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\n" ); document.write( " \"3%2Ax-28%2F2%2B%2836%2F4%29%2Ax=10\" Multiply
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\n" ); document.write( " \"3%2Ax-14%2B9%2Ax=10\" Reduce any fractions
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\n" ); document.write( " \"3%2Ax%2B9%2Ax=10%2B14\"Add \"14\" to both sides
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\n" ); document.write( " \"3%2Ax%2B9%2Ax=24\" Combine the terms on the right side
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\n" ); document.write( " \"12%2Ax=24\" Now combine the terms on the left side.
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\n" ); document.write( " \"cross%28%281%2F12%29%2812%2F1%29%29x=%2824%2F1%29%281%2F12%29\" Multiply both sides by \"1%2F12\". This will cancel out \"12%2F1\" and isolate x
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\n" ); document.write( " So when we multiply \"24%2F1\" and \"1%2F12\" (and simplify) we get
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\n" ); document.write( " \"x=2\" <---------------------------------One answer
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\n" ); document.write( " Now that we know that \"x=2\", lets substitute that in for x to solve for y
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\n" ); document.write( " \"3%282%29%2B4%2Ay=10\" Plug in \"x=2\" into the 2nd equation
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\n" ); document.write( " \"6%2B4%2Ay=10\" Multiply
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\n" ); document.write( " \"4%2Ay=10-6\"Subtract \"6\" from both sides
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\n" ); document.write( " \"4%2Ay=4\" Combine the terms on the right side
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\n" ); document.write( " \"cross%28%281%2F4%29%284%29%29%2Ay=%284%2F1%29%281%2F4%29\" Multiply both sides by \"1%2F4\". This will cancel out 4 on the left side.
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\n" ); document.write( " \"y=4%2F4\" Multiply the terms on the right side
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\n" ); document.write( " \"y=1\" Reduce
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\n" ); document.write( " So this is the other answer
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\n" ); document.write( " \"y=1\"<---------------------------------Other answer
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\n" ); document.write( " So our solution is
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\n" ); document.write( " \"x=2\" and \"y=1\"
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\n" ); document.write( " which can also look like
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\n" ); document.write( " (\"2\",\"1\")
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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( " \"9%2Ax-4%2Ay=14\"
\n" ); document.write( " \"3%2Ax%2B4%2Ay=10\"
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\n" ); document.write( " we get
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\n" ); document.write( " graph of \"9%2Ax-4%2Ay=14\" (red) and \"3%2Ax%2B4%2Ay=10\" (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 (\"2\",\"1\"). This verifies our answer.
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\n" ); document.write( " Check:
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\n" ); document.write( " Plug in (\"2\",\"1\") into the system of equations
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\n" ); document.write( " Let \"x=2\" and \"y=1\". Now plug those values into the equation \"9%2Ax-4%2Ay=14\"
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\n" ); document.write( " \"9%2A%282%29-4%2A%281%29=14\" Plug in \"x=2\" and \"y=1\"
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\n" ); document.write( " \"18-4=14\" Multiply
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\n" ); document.write( " \"14=14\" Add
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\n" ); document.write( " \"14=14\" Reduce. Since this equation is true the solution works.
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\n" ); document.write( " So the solution (\"2\",\"1\") satisfies \"9%2Ax-4%2Ay=14\"
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\n" ); document.write( " Let \"x=2\" and \"y=1\". Now plug those values into the equation \"3%2Ax%2B4%2Ay=10\"
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\n" ); document.write( " \"3%2A%282%29%2B4%2A%281%29=10\" Plug in \"x=2\" and \"y=1\"
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\n" ); document.write( " \"6%2B4=10\" Multiply
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\n" ); document.write( " \"10=10\" Add
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\n" ); document.write( " \"10=10\" Reduce. Since this equation is true the solution works.
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\n" ); document.write( " So the solution (\"2\",\"1\") satisfies \"3%2Ax%2B4%2Ay=10\"
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\n" ); document.write( " Since the solution (\"2\",\"1\") satisfies the system of equations
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\n" ); document.write( " \"9%2Ax-4%2Ay=14\"
\n" ); document.write( " \"3%2Ax%2B4%2Ay=10\"
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\n" ); document.write( " this verifies our answer.
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