document.write( "Question 99659: easy calc - Express vector w as...?\r
\n" ); document.write( "\n" ); document.write( " i know this is supposed to be a really easy question but i can't get to the right answer!! i know you're supposed to find a/b by elimination then sub but i keep getting the wrong answer...\r
\n" ); document.write( "\n" ); document.write( " heres the question:
\n" ); document.write( " Given the vectors u = [2,1] and v= [-1,3]:
\n" ); document.write( " a) Express the vector w = [12, -1] as a linear combination of vector u and v.\r
\n" ); document.write( "\n" ); document.write( " ANSWER: 5u - 2v\r
\n" ); document.write( "\n" ); document.write( " can someone explain / show work of how to do this please!!!\r
\n" ); document.write( "\n" ); document.write( " PS. all the letters have the little vector sign on them, just dunno how to do it on the computer lol.
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Algebra.Com's Answer #72522 by jim_thompson5910(35256)\"\" \"About 
You can put this solution on YOUR website!
Express the linear combination as a system of equations\r
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\n" ); document.write( "\n" ); document.write( "2x-y=12\r
\n" ); document.write( "\n" ); document.write( "-x+3y=-1\r
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\n" ); document.write( "\n" ); document.write( "Now solve the system using substitution:\r
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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-1%2Ay=12\"
\n" ); document.write( " \"1%2Ax%2B3%2Ay=-1\"
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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=12-2%2Ax\"Subtract \"2%2Ax\" from both sides
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\n" ); document.write( " \"y=%2812-2%2Ax%29%2F-1\" 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=-12%2B2%2Ax\" Now we've fully isolated y
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\n" ); document.write( " Since y equals \"-12%2B2%2Ax\" we can substitute the expression \"-12%2B2%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%2B3%2Ahighlight%28%28-12%2B2%2Ax%29%29=-1\" Replace y with \"-12%2B2%2Ax\". Since this eliminates y, we can now solve for x.
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\n" ); document.write( " \"1%2Ax%2B3%2A%28-12%29%2B3%282%29x=-1\" Distribute 3 to \"-12%2B2%2Ax\"
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\n" ); document.write( " \"1%2Ax-36%2B6%2Ax=-1\" Multiply
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\n" ); document.write( " \"1%2Ax-36%2B6%2Ax=-1\" Reduce any fractions
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\n" ); document.write( " \"1%2Ax%2B6%2Ax=-1%2B36\"Add \"36\" to both sides
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\n" ); document.write( " \"1%2Ax%2B6%2Ax=35\" Combine the terms on the right side
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\n" ); document.write( " \"7%2Ax=35\" Now combine the terms on the left side.
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\n" ); document.write( " \"cross%28%281%2F7%29%287%2F1%29%29x=%2835%2F1%29%281%2F7%29\" Multiply both sides by \"1%2F7\". This will cancel out \"7%2F1\" and isolate x
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\n" ); document.write( " So when we multiply \"35%2F1\" and \"1%2F7\" (and simplify) we get
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\n" ); document.write( " \"x=5\" <---------------------------------One answer
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\n" ); document.write( " Now that we know that \"x=5\", lets substitute that in for x to solve for y
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\n" ); document.write( " \"1%285%29%2B3%2Ay=-1\" Plug in \"x=5\" into the 2nd equation
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\n" ); document.write( " \"5%2B3%2Ay=-1\" Multiply
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\n" ); document.write( " \"3%2Ay=-1-5\"Subtract \"5\" from both sides
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\n" ); document.write( " \"3%2Ay=-6\" Combine the terms on the right side
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\n" ); document.write( " \"cross%28%281%2F3%29%283%29%29%2Ay=%28-6%2F1%29%281%2F3%29\" Multiply both sides by \"1%2F3\". This will cancel out 3 on the left side.
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\n" ); document.write( " \"y=-6%2F3\" Multiply the terms on the right side
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\n" ); document.write( " \"y=-2\" Reduce
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\n" ); document.write( " So this is the other answer
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\n" ); document.write( " \"y=-2\"<---------------------------------Other answer
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\n" ); document.write( " So our solution is
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\n" ); document.write( " \"x=5\" and \"y=-2\"
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\n" ); document.write( " which can also look like
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\n" ); document.write( " (\"5\",\"-2\")
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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-1%2Ay=12\"
\n" ); document.write( " \"1%2Ax%2B3%2Ay=-1\"
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\n" ); document.write( " we get
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\n" ); document.write( " graph of \"2%2Ax-1%2Ay=12\" (red) and \"1%2Ax%2B3%2Ay=-1\" (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\",\"-2\"). This verifies our answer.
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\n" ); document.write( " -----------------------------------------------------------------------------------------------
\n" ); document.write( " Check:
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\n" ); document.write( " Plug in (\"5\",\"-2\") into the system of equations
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\n" ); document.write( " Let \"x=5\" and \"y=-2\". Now plug those values into the equation \"2%2Ax-1%2Ay=12\"
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\n" ); document.write( " \"2%2A%285%29-1%2A%28-2%29=12\" Plug in \"x=5\" and \"y=-2\"
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\n" ); document.write( "
\n" ); document.write( " \"10%2B2=12\" Multiply
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\n" ); document.write( " \"12=12\" Add
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\n" ); document.write( " \"12=12\" Reduce. Since this equation is true the solution works.
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\n" ); document.write( " So the solution (\"5\",\"-2\") satisfies \"2%2Ax-1%2Ay=12\"
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\n" ); document.write( " Let \"x=5\" and \"y=-2\". Now plug those values into the equation \"1%2Ax%2B3%2Ay=-1\"
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\n" ); document.write( " \"1%2A%285%29%2B3%2A%28-2%29=-1\" Plug in \"x=5\" and \"y=-2\"
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\n" ); document.write( "
\n" ); document.write( " \"5-6=-1\" Multiply
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\n" ); document.write( "
\n" ); document.write( " \"-1=-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\",\"-2\") satisfies \"1%2Ax%2B3%2Ay=-1\"
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\n" ); document.write( "
\n" ); document.write( " Since the solution (\"5\",\"-2\") satisfies the system of equations
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\n" ); document.write( " \"2%2Ax-1%2Ay=12\"
\n" ); document.write( " \"1%2Ax%2B3%2Ay=-1\"
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\n" ); document.write( " this verifies our answer.
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\n" ); document.write( "\n" ); document.write( "So x=5, y=-2 translates to 5u-2v
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