document.write( "Question 120188: Use substitution or elimination to solve each system of equations. Please explain.
\n" ); document.write( "
\n" ); document.write( "7. 2x + 5y=16
\n" ); document.write( " 5x - 2y= 11
\n" ); document.write( "

Algebra.Com's Answer #88063 by jim_thompson5910(35256)\"\" \"About 
You can put this solution on YOUR website!
\n" ); document.write( "\n" ); document.write( " \n" ); document.write( "\n" ); document.write( "
Solved by pluggable solver: Solving a linear system of equations by subsitution

\n" ); document.write( "
\n" ); document.write( " Lets start with the given system of linear equations
\n" ); document.write( "
\n" ); document.write( " \"2%2Ax%2B5%2Ay=16\"
\n" ); document.write( " \"5%2Ax-2%2Ay=11\"
\n" ); document.write( "
\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.
\n" ); document.write( "
\n" ); document.write( " Solve for y for the first equation
\n" ); document.write( "
\n" ); document.write( " \"5%2Ay=16-2%2Ax\"Subtract \"2%2Ax\" from both sides
\n" ); document.write( "
\n" ); document.write( " \"y=%2816-2%2Ax%29%2F5\" Divide both sides by 5.
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " Which breaks down and reduces to
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"y=16%2F5-%282%2F5%29%2Ax\" Now we've fully isolated y
\n" ); document.write( "
\n" ); document.write( " Since y equals \"16%2F5-%282%2F5%29%2Ax\" we can substitute the expression \"16%2F5-%282%2F5%29%2Ax\" into y of the 2nd equation. This will eliminate y so we can solve for x.
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"5%2Ax%2B-2%2Ahighlight%28%2816%2F5-%282%2F5%29%2Ax%29%29=11\" Replace y with \"16%2F5-%282%2F5%29%2Ax\". Since this eliminates y, we can now solve for x.
\n" ); document.write( "
\n" ); document.write( " \"5%2Ax-2%2A%2816%2F5%29-2%28-2%2F5%29x=11\" Distribute -2 to \"16%2F5-%282%2F5%29%2Ax\"
\n" ); document.write( "
\n" ); document.write( " \"5%2Ax-32%2F5%2B%284%2F5%29%2Ax=11\" Multiply
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"5%2Ax-32%2F5%2B%284%2F5%29%2Ax=11\" Reduce any fractions
\n" ); document.write( "
\n" ); document.write( " \"5%2Ax%2B%284%2F5%29%2Ax=11%2B32%2F5\"Add \"32%2F5\" to both sides
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"5%2Ax%2B%284%2F5%29%2Ax=55%2F5%2B32%2F5\" Make 11 into a fraction with a denominator of 5
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"5%2Ax%2B%284%2F5%29%2Ax=87%2F5\" Combine the terms on the right side
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"%2825%2F5%29%2Ax%2B%284%2F5%29x=87%2F5\" Make 5 into a fraction with a denominator of 5
\n" ); document.write( "
\n" ); document.write( " \"%2829%2F5%29%2Ax=87%2F5\" Now combine the terms on the left side.
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"cross%28%285%2F29%29%2829%2F5%29%29x=%2887%2F5%29%285%2F29%29\" Multiply both sides by \"5%2F29\". This will cancel out \"29%2F5\" and isolate x
\n" ); document.write( "
\n" ); document.write( " So when we multiply \"87%2F5\" and \"5%2F29\" (and simplify) we get
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"x=3\" <---------------------------------One answer
\n" ); document.write( "
\n" ); document.write( " Now that we know that \"x=3\", lets substitute that in for x to solve for y
\n" ); document.write( "
\n" ); document.write( " \"5%283%29-2%2Ay=11\" Plug in \"x=3\" into the 2nd equation
\n" ); document.write( "
\n" ); document.write( " \"15-2%2Ay=11\" Multiply
\n" ); document.write( "
\n" ); document.write( " \"-2%2Ay=11-15\"Subtract \"15\" from both sides
\n" ); document.write( "
\n" ); document.write( " \"-2%2Ay=-4\" Combine the terms on the right side
\n" ); document.write( "
\n" ); document.write( " \"cross%28%281%2F-2%29%28-2%29%29%2Ay=%28-4%2F1%29%281%2F-2%29\" Multiply both sides by \"1%2F-2\". This will cancel out -2 on the left side.
\n" ); document.write( "
\n" ); document.write( " \"y=-4%2F-2\" Multiply the terms on the right side
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"y=2\" Reduce
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " So this is the other answer
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"y=2\"<---------------------------------Other answer
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " So our solution is
\n" ); document.write( "
\n" ); document.write( " \"x=3\" and \"y=2\"
\n" ); document.write( "
\n" ); document.write( " which can also look like
\n" ); document.write( "
\n" ); document.write( " (\"3\",\"2\")
\n" ); document.write( "
\n" ); document.write( " Notice if we graph the equations (if you need help with graphing, check out this solver)
\n" ); document.write( "
\n" ); document.write( " \"2%2Ax%2B5%2Ay=16\"
\n" ); document.write( " \"5%2Ax-2%2Ay=11\"
\n" ); document.write( "
\n" ); document.write( " we get
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " graph of \"2%2Ax%2B5%2Ay=16\" (red) and \"5%2Ax-2%2Ay=11\" (green) (hint: you may have to solve for y to graph these) intersecting at the blue circle.
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " and we can see that the two equations intersect at (\"3\",\"2\"). This verifies our answer.
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " -----------------------------------------------------------------------------------------------
\n" ); document.write( " Check:
\n" ); document.write( "
\n" ); document.write( " Plug in (\"3\",\"2\") into the system of equations
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " Let \"x=3\" and \"y=2\". Now plug those values into the equation \"2%2Ax%2B5%2Ay=16\"
\n" ); document.write( "
\n" ); document.write( " \"2%2A%283%29%2B5%2A%282%29=16\" Plug in \"x=3\" and \"y=2\"
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"6%2B10=16\" Multiply
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"16=16\" Add
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"16=16\" Reduce. Since this equation is true the solution works.
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " So the solution (\"3\",\"2\") satisfies \"2%2Ax%2B5%2Ay=16\"
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " Let \"x=3\" and \"y=2\". Now plug those values into the equation \"5%2Ax-2%2Ay=11\"
\n" ); document.write( "
\n" ); document.write( " \"5%2A%283%29-2%2A%282%29=11\" Plug in \"x=3\" and \"y=2\"
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"15-4=11\" Multiply
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"11=11\" Add
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"11=11\" Reduce. Since this equation is true the solution works.
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " So the solution (\"3\",\"2\") satisfies \"5%2Ax-2%2Ay=11\"
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " Since the solution (\"3\",\"2\") satisfies the system of equations
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"2%2Ax%2B5%2Ay=16\"
\n" ); document.write( " \"5%2Ax-2%2Ay=11\"
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " this verifies our answer.
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" );