document.write( "Question 112352: I need help solving this system by substitution and elimination.\r
\n" ); document.write( "\n" ); document.write( "-16x+45y=134
\n" ); document.write( "40x+18y=-45\r
\n" ); document.write( "\n" ); document.write( "
\n" ); document.write( "

Algebra.Com's Answer #81975 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( " \"-16%2Ax%2B45%2Ay=134\"
\n" ); document.write( " \"40%2Ax%2B18%2Ay=-45\"
\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( " \"45%2Ay=134%2B16%2Ax\"Add \"16%2Ax\" to both sides
\n" ); document.write( "
\n" ); document.write( " \"y=%28134%2B16%2Ax%29%2F45\" Divide both sides by 45.
\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=134%2F45%2B%2816%2F45%29%2Ax\" Now we've fully isolated y
\n" ); document.write( "
\n" ); document.write( " Since y equals \"134%2F45%2B%2816%2F45%29%2Ax\" we can substitute the expression \"134%2F45%2B%2816%2F45%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( " \"40%2Ax%2B18%2Ahighlight%28%28134%2F45%2B%2816%2F45%29%2Ax%29%29=-45\" Replace y with \"134%2F45%2B%2816%2F45%29%2Ax\". Since this eliminates y, we can now solve for x.
\n" ); document.write( "
\n" ); document.write( " \"40%2Ax%2B18%2A%28134%2F45%29%2B18%2816%2F45%29x=-45\" Distribute 18 to \"134%2F45%2B%2816%2F45%29%2Ax\"
\n" ); document.write( "
\n" ); document.write( " \"40%2Ax%2B2412%2F45%2B%28288%2F45%29%2Ax=-45\" Multiply
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"40%2Ax%2B268%2F5%2B%2832%2F5%29%2Ax=-45\" Reduce any fractions
\n" ); document.write( "
\n" ); document.write( " \"40%2Ax%2B%2832%2F5%29%2Ax=-45-268%2F5\" Subtract \"268%2F5\" from both sides
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"40%2Ax%2B%2832%2F5%29%2Ax=-225%2F5-268%2F5\" Make -45 into a fraction with a denominator of 5
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"40%2Ax%2B%2832%2F5%29%2Ax=-493%2F5\" Combine the terms on the right side
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"%28200%2F5%29%2Ax%2B%2832%2F5%29x=-493%2F5\" Make 40 into a fraction with a denominator of 5
\n" ); document.write( "
\n" ); document.write( " \"%28232%2F5%29%2Ax=-493%2F5\" Now combine the terms on the left side.
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"cross%28%285%2F232%29%28232%2F5%29%29x=%28-493%2F5%29%285%2F232%29\" Multiply both sides by \"5%2F232\". This will cancel out \"232%2F5\" and isolate x
\n" ); document.write( "
\n" ); document.write( " So when we multiply \"-493%2F5\" and \"5%2F232\" (and simplify) we get
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"x=-17%2F8\" <---------------------------------One answer
\n" ); document.write( "
\n" ); document.write( " Now that we know that \"x=-17%2F8\", lets substitute that in for x to solve for y
\n" ); document.write( "
\n" ); document.write( " \"40%28-17%2F8%29%2B18%2Ay=-45\" Plug in \"x=-17%2F8\" into the 2nd equation
\n" ); document.write( "
\n" ); document.write( " \"-85%2B18%2Ay=-45\" Multiply
\n" ); document.write( "
\n" ); document.write( " \"18%2Ay=-45%2B85\"Add \"85\" to both sides
\n" ); document.write( "
\n" ); document.write( " \"18%2Ay=40\" Combine the terms on the right side
\n" ); document.write( "
\n" ); document.write( " \"cross%28%281%2F18%29%2818%29%29%2Ay=%2840%2F1%29%281%2F18%29\" Multiply both sides by \"1%2F18\". This will cancel out 18 on the left side.
\n" ); document.write( "
\n" ); document.write( " \"y=40%2F18\" Multiply the terms on the right side
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"y=20%2F9\" 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=20%2F9\"<---------------------------------Other answer
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " So our solution is
\n" ); document.write( "
\n" ); document.write( " \"x=-17%2F8\" and \"y=20%2F9\"
\n" ); document.write( "
\n" ); document.write( " which can also look like
\n" ); document.write( "
\n" ); document.write( " (\"-17%2F8\",\"20%2F9\")
\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( " \"-16%2Ax%2B45%2Ay=134\"
\n" ); document.write( " \"40%2Ax%2B18%2Ay=-45\"
\n" ); document.write( "
\n" ); document.write( " we get
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " graph of \"-16%2Ax%2B45%2Ay=134\" (red) and \"40%2Ax%2B18%2Ay=-45\" (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 (\"-17%2F8\",\"20%2F9\"). 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 (\"-17%2F8\",\"20%2F9\") into the system of equations
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " Let \"x=-17%2F8\" and \"y=20%2F9\". Now plug those values into the equation \"-16%2Ax%2B45%2Ay=134\"
\n" ); document.write( "
\n" ); document.write( " \"-16%2A%28-17%2F8%29%2B45%2A%2820%2F9%29=134\" Plug in \"x=-17%2F8\" and \"y=20%2F9\"
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"272%2F8%2B900%2F9=134\" Multiply
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"9648%2F72=134\" Add
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"134=134\" Reduce. Since this equation is true the solution works.
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " So the solution (\"-17%2F8\",\"20%2F9\") satisfies \"-16%2Ax%2B45%2Ay=134\"
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " Let \"x=-17%2F8\" and \"y=20%2F9\". Now plug those values into the equation \"40%2Ax%2B18%2Ay=-45\"
\n" ); document.write( "
\n" ); document.write( " \"40%2A%28-17%2F8%29%2B18%2A%2820%2F9%29=-45\" Plug in \"x=-17%2F8\" and \"y=20%2F9\"
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"-680%2F8%2B360%2F9=-45\" Multiply
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"-3240%2F72=-45\" Add
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"-45=-45\" Reduce. Since this equation is true the solution works.
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " So the solution (\"-17%2F8\",\"20%2F9\") satisfies \"40%2Ax%2B18%2Ay=-45\"
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " Since the solution (\"-17%2F8\",\"20%2F9\") satisfies the system of equations
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( " \"-16%2Ax%2B45%2Ay=134\"
\n" ); document.write( " \"40%2Ax%2B18%2Ay=-45\"
\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" );