document.write( "Question 111439: Solve the system by substitution.
\n" ); document.write( " x – 3y = 14
\n" ); document.write( " –3x + 5y = –14
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Algebra.Com's Answer #81265 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( " \"1%2Ax-3%2Ay=14\"
\n" ); document.write( " \"-3%2Ax%2B5%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( " \"-3%2Ay=14-1%2Ax\"Subtract \"1%2Ax\" from both sides
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\n" ); document.write( " \"y=%2814-1%2Ax%29%2F-3\" Divide both sides by -3.
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\n" ); document.write( " Which breaks down and reduces to
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\n" ); document.write( " \"y=-14%2F3%2B%281%2F3%29%2Ax\" Now we've fully isolated y
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\n" ); document.write( " Since y equals \"-14%2F3%2B%281%2F3%29%2Ax\" we can substitute the expression \"-14%2F3%2B%281%2F3%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%2B5%2Ahighlight%28%28-14%2F3%2B%281%2F3%29%2Ax%29%29=-14\" Replace y with \"-14%2F3%2B%281%2F3%29%2Ax\". Since this eliminates y, we can now solve for x.
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\n" ); document.write( " \"-3%2Ax%2B5%2A%28-14%2F3%29%2B5%281%2F3%29x=-14\" Distribute 5 to \"-14%2F3%2B%281%2F3%29%2Ax\"
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\n" ); document.write( " \"-3%2Ax-70%2F3%2B%285%2F3%29%2Ax=-14\" Multiply
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\n" ); document.write( " \"-3%2Ax-70%2F3%2B%285%2F3%29%2Ax=-14\" Reduce any fractions
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\n" ); document.write( " \"-3%2Ax%2B%285%2F3%29%2Ax=-14%2B70%2F3\"Add \"70%2F3\" to both sides
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\n" ); document.write( " \"-3%2Ax%2B%285%2F3%29%2Ax=-42%2F3%2B70%2F3\" Make -14 into a fraction with a denominator of 3
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\n" ); document.write( " \"-3%2Ax%2B%285%2F3%29%2Ax=28%2F3\" Combine the terms on the right side
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\n" ); document.write( " \"%28-9%2F3%29%2Ax%2B%285%2F3%29x=28%2F3\" Make -3 into a fraction with a denominator of 3
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\n" ); document.write( " \"%28-4%2F3%29%2Ax=28%2F3\" Now combine the terms on the left side.
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\n" ); document.write( " \"cross%28%283%2F-4%29%28-4%2F3%29%29x=%2828%2F3%29%283%2F-4%29\" Multiply both sides by \"3%2F-4\". This will cancel out \"-4%2F3\" and isolate x
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\n" ); document.write( " So when we multiply \"28%2F3\" and \"3%2F-4\" (and simplify) we get
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\n" ); document.write( " \"x=-7\" <---------------------------------One answer
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\n" ); document.write( " Now that we know that \"x=-7\", lets substitute that in for x to solve for y
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\n" ); document.write( " \"-3%28-7%29%2B5%2Ay=-14\" Plug in \"x=-7\" into the 2nd equation
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\n" ); document.write( " \"21%2B5%2Ay=-14\" Multiply
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\n" ); document.write( " \"5%2Ay=-14-21\"Subtract \"21\" from both sides
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\n" ); document.write( " \"5%2Ay=-35\" Combine the terms on the right side
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\n" ); document.write( " \"cross%28%281%2F5%29%285%29%29%2Ay=%28-35%2F1%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( " \"y=-35%2F5\" Multiply the terms on the right side
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\n" ); document.write( " \"y=-7\" Reduce
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\n" ); document.write( " So this is the other answer
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\n" ); document.write( " \"y=-7\"<---------------------------------Other answer
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\n" ); document.write( " So our solution is
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\n" ); document.write( " \"x=-7\" and \"y=-7\"
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\n" ); document.write( " which can also look like
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\n" ); document.write( " (\"-7\",\"-7\")
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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( " \"1%2Ax-3%2Ay=14\"
\n" ); document.write( " \"-3%2Ax%2B5%2Ay=-14\"
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\n" ); document.write( " we get
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\n" ); document.write( " graph of \"1%2Ax-3%2Ay=14\" (red) and \"-3%2Ax%2B5%2Ay=-14\" (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 (\"-7\",\"-7\"). This verifies our answer.
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\n" ); document.write( " Check:
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\n" ); document.write( " Plug in (\"-7\",\"-7\") into the system of equations
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\n" ); document.write( " Let \"x=-7\" and \"y=-7\". Now plug those values into the equation \"1%2Ax-3%2Ay=14\"
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\n" ); document.write( " \"1%2A%28-7%29-3%2A%28-7%29=14\" Plug in \"x=-7\" and \"y=-7\"
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\n" ); document.write( " \"-7%2B21=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 (\"-7\",\"-7\") satisfies \"1%2Ax-3%2Ay=14\"
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\n" ); document.write( "
\n" ); document.write( " Let \"x=-7\" and \"y=-7\". Now plug those values into the equation \"-3%2Ax%2B5%2Ay=-14\"
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\n" ); document.write( " \"-3%2A%28-7%29%2B5%2A%28-7%29=-14\" Plug in \"x=-7\" and \"y=-7\"
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\n" ); document.write( " \"21-35=-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 (\"-7\",\"-7\") satisfies \"-3%2Ax%2B5%2Ay=-14\"
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\n" ); document.write( " Since the solution (\"-7\",\"-7\") satisfies the system of equations
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\n" ); document.write( " \"1%2Ax-3%2Ay=14\"
\n" ); document.write( " \"-3%2Ax%2B5%2Ay=-14\"
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\n" ); document.write( " this verifies our answer.
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