document.write( "Question 86915: If the sum of two numbers is 1, and their difference is 4, what are the two numbers? \n" ); document.write( "
Algebra.Com's Answer #62857 by jim_thompson5910(35256)\"\" \"About 
You can put this solution on YOUR website!
Let x=1st #, y=2nd #\r
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\n" ); document.write( "\n" ); document.write( "After translation, we get the system of equations:\r
\n" ); document.write( "\n" ); document.write( "\"x%2By=1\" \"the sum of two numbers is 1\"
\n" ); document.write( "\"x-y=4\" \"their difference is 4\"
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\n" ); document.write( "\n" ); document.write( "Now lets solve this system by using substitution
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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%2B1%2Ay=1\"
\n" ); document.write( " \"1%2Ax-1%2Ay=4\"
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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( " \"1%2Ay=1-1%2Ax\"Subtract \"1%2Ax\" from both sides
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\n" ); document.write( " \"y=%281-1%2Ax%29\" Divide both sides by 1.
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\n" ); document.write( " Which breaks down and reduces to
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\n" ); document.write( " \"y=1-1%2Ax\" Now we've fully isolated y
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\n" ); document.write( " Since y equals \"1-1%2Ax\" we can substitute the expression \"1-1%2Ax\" into y of the 2nd equation. This will eliminate y so we can solve for x.
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\n" ); document.write( " \"1%2Ax%2B-1%2Ahighlight%28%281-1%2Ax%29%29=4\" Replace y with \"1-1%2Ax\". Since this eliminates y, we can now solve for x.
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\n" ); document.write( " \"1%2Ax-1%2A%281%29-1%28-1%29x=4\" Distribute -1 to \"1-1%2Ax\"
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\n" ); document.write( " \"1%2Ax-1%2B1%2Ax=4\" Multiply
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\n" ); document.write( " \"1%2Ax-1%2B1%2Ax=4\" Reduce any fractions
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\n" ); document.write( " \"1%2Ax%2B1%2Ax=4%2B1\"Add \"1\" to both sides
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\n" ); document.write( " \"1%2Ax%2B1%2Ax=5\" Combine the terms on the right side
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\n" ); document.write( " \"2%2Ax=5\" Now combine the terms on the left side.
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\n" ); document.write( " \"cross%28%281%2F2%29%282%2F1%29%29x=%285%2F1%29%281%2F2%29\" Multiply both sides by \"1%2F2\". This will cancel out \"2%2F1\" and isolate x
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\n" ); document.write( " So when we multiply \"5%2F1\" and \"1%2F2\" (and simplify) we get
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\n" ); document.write( " \"x=5%2F2\" <---------------------------------One answer
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\n" ); document.write( " Now that we know that \"x=5%2F2\", lets substitute that in for x to solve for y
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\n" ); document.write( " \"1%285%2F2%29-1%2Ay=4\" Plug in \"x=5%2F2\" into the 2nd equation
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\n" ); document.write( " \"5%2F2-1%2Ay=4\" Multiply
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\n" ); document.write( " \"-1%2Ay=4-5%2F2\"Subtract \"5%2F2\" from both sides
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\n" ); document.write( " \"-1%2Ay=8%2F2-5%2F2\" Make 4 into a fraction with a denominator of 2
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\n" ); document.write( " \"-1%2Ay=3%2F2\" Combine the terms on the right side
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\n" ); document.write( " \"cross%28%281%2F-1%29%28-1%29%29%2Ay=%283%2F2%29%281%2F-1%29\" Multiply both sides by \"1%2F-1\". This will cancel out -1 on the left side.
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\n" ); document.write( " \"y=3%2F-2\" Multiply the terms on the right side
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\n" ); document.write( " \"y=-3%2F2\" Reduce
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\n" ); document.write( " So this is the other answer
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\n" ); document.write( " \"y=-3%2F2\"<---------------------------------Other answer
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\n" ); document.write( " So our solution is
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\n" ); document.write( " \"x=5%2F2\" and \"y=-3%2F2\"
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\n" ); document.write( " which can also look like
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\n" ); document.write( " (\"5%2F2\",\"-3%2F2\")
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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%2B1%2Ay=1\"
\n" ); document.write( " \"1%2Ax-1%2Ay=4\"
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\n" ); document.write( " we get
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\n" ); document.write( " graph of \"1%2Ax%2B1%2Ay=1\" (red) and \"1%2Ax-1%2Ay=4\" (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 (\"5%2F2\",\"-3%2F2\"). This verifies our answer.
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\n" ); document.write( " Check:
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\n" ); document.write( " Plug in (\"5%2F2\",\"-3%2F2\") into the system of equations
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\n" ); document.write( " Let \"x=5%2F2\" and \"y=-3%2F2\". Now plug those values into the equation \"1%2Ax%2B1%2Ay=1\"
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\n" ); document.write( " \"1%2A%285%2F2%29%2B1%2A%28-3%2F2%29=1\" Plug in \"x=5%2F2\" and \"y=-3%2F2\"
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\n" ); document.write( " \"5%2F2-3%2F2=1\" Multiply
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\n" ); document.write( " \"2%2F2=1\" Add
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\n" ); document.write( " \"1=1\" Reduce. Since this equation is true the solution works.
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\n" ); document.write( " So the solution (\"5%2F2\",\"-3%2F2\") satisfies \"1%2Ax%2B1%2Ay=1\"
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\n" ); document.write( " Let \"x=5%2F2\" and \"y=-3%2F2\". Now plug those values into the equation \"1%2Ax-1%2Ay=4\"
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\n" ); document.write( " \"1%2A%285%2F2%29-1%2A%28-3%2F2%29=4\" Plug in \"x=5%2F2\" and \"y=-3%2F2\"
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\n" ); document.write( " \"5%2F2%2B3%2F2=4\" Multiply
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\n" ); document.write( " \"8%2F2=4\" Add
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\n" ); document.write( " \"4=4\" Reduce. Since this equation is true the solution works.
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\n" ); document.write( " So the solution (\"5%2F2\",\"-3%2F2\") satisfies \"1%2Ax-1%2Ay=4\"
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\n" ); document.write( " Since the solution (\"5%2F2\",\"-3%2F2\") satisfies the system of equations
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\n" ); document.write( " \"1%2Ax%2B1%2Ay=1\"
\n" ); document.write( " \"1%2Ax-1%2Ay=4\"
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\n" ); document.write( " this verifies our answer.
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\n" ); document.write( "\n" ); document.write( "Since \"x=5%2F2\" and \"y=-3%2F2\" this means our first number is \"5%2F2\" and our second number is\"-3%2F2\"
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