document.write( "Question 1190343: I am really having a hard time understanding solving using substitution \r
\n" ); document.write( "\n" ); document.write( "2x+3y=24
\n" ); document.write( "-3x-5y=15\r
\n" ); document.write( "\n" ); document.write( "how do I solve those using substitution
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Algebra.Com's Answer #821958 by MathLover1(20850)\"\" \"About 
You can put this solution on YOUR website!

\n" ); document.write( "\"2x%2B3y=24\".....eq.1
\n" ); document.write( "\"-3x-5y=15\"....eq.2
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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( " \"2%2Ax%2B3%2Ay=24\"
\n" ); document.write( " \"-3%2Ax-5%2Ay=15\"
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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=24-2%2Ax\"Subtract \"2%2Ax\" from both sides
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\n" ); document.write( " \"y=%2824-2%2Ax%29%2F3\" 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=8-%282%2F3%29%2Ax\" Now we've fully isolated y
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\n" ); document.write( " Since y equals \"8-%282%2F3%29%2Ax\" we can substitute the expression \"8-%282%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%2B-5%2Ahighlight%28%288-%282%2F3%29%2Ax%29%29=15\" Replace y with \"8-%282%2F3%29%2Ax\". Since this eliminates y, we can now solve for x.
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\n" ); document.write( " \"-3%2Ax-5%2A%288%29-5%28-2%2F3%29x=15\" Distribute -5 to \"8-%282%2F3%29%2Ax\"
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\n" ); document.write( " \"-3%2Ax-40%2B%2810%2F3%29%2Ax=15\" Multiply
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\n" ); document.write( " \"-3%2Ax-40%2B%2810%2F3%29%2Ax=15\" Reduce any fractions
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\n" ); document.write( " \"-3%2Ax%2B%2810%2F3%29%2Ax=15%2B40\"Add \"40\" to both sides
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\n" ); document.write( " \"-3%2Ax%2B%2810%2F3%29%2Ax=55\" Combine the terms on the right side
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\n" ); document.write( " \"%28-9%2F3%29%2Ax%2B%2810%2F3%29x=55\" Make -3 into a fraction with a denominator of 3
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\n" ); document.write( " \"%281%2F3%29%2Ax=55\" Now combine the terms on the left side.
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\n" ); document.write( " \"cross%28%283%2F1%29%281%2F3%29%29x=%2855%2F1%29%283%2F1%29\" Multiply both sides by \"3%2F1\". This will cancel out \"1%2F3\" and isolate x
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\n" ); document.write( " So when we multiply \"55%2F1\" and \"3%2F1\" (and simplify) we get
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\n" ); document.write( " \"x=165\" <---------------------------------One answer
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\n" ); document.write( " Now that we know that \"x=165\", lets substitute that in for x to solve for y
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\n" ); document.write( " \"-3%28165%29-5%2Ay=15\" Plug in \"x=165\" into the 2nd equation
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\n" ); document.write( " \"-495-5%2Ay=15\" Multiply
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\n" ); document.write( " \"-5%2Ay=15%2B495\"Add \"495\" to both sides
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\n" ); document.write( " \"-5%2Ay=510\" Combine the terms on the right side
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\n" ); document.write( " \"cross%28%281%2F-5%29%28-5%29%29%2Ay=%28510%2F1%29%281%2F-5%29\" Multiply both sides by \"1%2F-5\". This will cancel out -5 on the left side.
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\n" ); document.write( " \"y=510%2F-5\" Multiply the terms on the right side
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\n" ); document.write( " \"y=-102\" Reduce
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\n" ); document.write( " So this is the other answer
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\n" ); document.write( " \"y=-102\"<---------------------------------Other answer
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\n" ); document.write( " So our solution is
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\n" ); document.write( " \"x=165\" and \"y=-102\"
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\n" ); document.write( " which can also look like
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\n" ); document.write( " (\"165\",\"-102\")
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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( " \"2%2Ax%2B3%2Ay=24\"
\n" ); document.write( " \"-3%2Ax-5%2Ay=15\"
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\n" ); document.write( " we get
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\n" ); document.write( " graph of \"2%2Ax%2B3%2Ay=24\" (red) and \"-3%2Ax-5%2Ay=15\" (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 (\"165\",\"-102\"). This verifies our answer.
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\n" ); document.write( " Plug in (\"165\",\"-102\") into the system of equations
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\n" ); document.write( " Let \"x=165\" and \"y=-102\". Now plug those values into the equation \"2%2Ax%2B3%2Ay=24\"
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\n" ); document.write( " \"2%2A%28165%29%2B3%2A%28-102%29=24\" Plug in \"x=165\" and \"y=-102\"
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\n" ); document.write( " \"330-306=24\" Multiply
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\n" ); document.write( " \"24=24\" Add
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\n" ); document.write( " \"24=24\" Reduce. Since this equation is true the solution works.
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\n" ); document.write( " So the solution (\"165\",\"-102\") satisfies \"2%2Ax%2B3%2Ay=24\"
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\n" ); document.write( " Let \"x=165\" and \"y=-102\". Now plug those values into the equation \"-3%2Ax-5%2Ay=15\"
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\n" ); document.write( " \"-3%2A%28165%29-5%2A%28-102%29=15\" Plug in \"x=165\" and \"y=-102\"
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\n" ); document.write( " \"-495%2B510=15\" Multiply
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\n" ); document.write( " \"15=15\" Add
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\n" ); document.write( " \"15=15\" Reduce. Since this equation is true the solution works.
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\n" ); document.write( " So the solution (\"165\",\"-102\") satisfies \"-3%2Ax-5%2Ay=15\"
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\n" ); document.write( " Since the solution (\"165\",\"-102\") satisfies the system of equations
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\n" ); document.write( " \"2%2Ax%2B3%2Ay=24\"
\n" ); document.write( " \"-3%2Ax-5%2Ay=15\"
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\n" ); document.write( " this verifies our answer.
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