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Math Help - Would someone be so kind as to help me?

  1. #1
    Newbie Silverstaraptor's Avatar
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    Exclamation Would someone be so kind as to help me?

    I have been stuck on this ssooooo long....
    instuctions: solve the linear system using elimination. PLEASE!! SOMEONE SAVE ME!!!!

    9x + y = 2

    -4x - y = -17
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  2. #2
    Senior Member mollymcf2009's Avatar
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    Quote Originally Posted by Silverstaraptor View Post
    I have been stuck on this ssooooo long....
    instuctions: solve the linear system using elimination. PLEASE!! SOMEONE SAVE ME!!!!

    9x + y = 2

    -4x - y = -17
    Hello!

    You are given two equations, both containing a x & y value. You can use one of the equations to isolate one of the variables and then substitute it into the other equation so you will have only one variable to solve for.

    So using

    9x + y = 2
    and
    -4x - y = -17

    Let's choose the one that looks the easiest to solve for a variable. I think the first one looks good.

    Let's solve for y:

    y = 2 - 9x

    So do you see that we have a value for y in terms of x?

    Now we can plug this into the second equation to get rid of the y:

    -4x - (2-9x) = -17

    Now you can find out what x is. Once you have a numerical value for x, you can plug that number back into either of the equations and find your y value. Okay? Good luck!!

    OOPS! Sorry I solved it using substitution. To solve it using elimination, just add the two equations. Put one on top of the other and solve it just like a regular addition problem. You will see that this gets rid of your y values. Then you can plug whatever you get for x into either of the equations and find your y value. Ok? sorry I read it wrong!!
    Last edited by mollymcf2009; March 3rd 2009 at 07:46 PM. Reason: Wrong technique
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  3. #3
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    answer to your prayer

    Alright holmes, here is how you do it. You need to add equation 2 (-4x-y= -17) to equation 1 (9x+y= 2), or vice versa, it doesnt matter just add the two equations. So it would be 9x+(-4x)+y+(-y)= 2+(-17). So now the y's cancel and you are left with the equation 5x= -15. solve and x=-3. Plug in -3 to either equation to solve for y. Both equations result in y=29. If you ever get different answers for the same variable (say y=22 and y=14) then you have made a mistake. Im out.
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  4. #4
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    Quote Originally Posted by Silverstaraptor View Post
    I have been stuck on this ssooooo long....
    instuctions: solve the linear system using elimination. PLEASE!! SOMEONE SAVE ME!!!!

    9x + y = 2

    -4x - y = -17
    Add the two equations:

    5x = -15 => x = -3. Now solve for y.
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  5. #5
    Newbie Silverstaraptor's Avatar
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    I'm totally hopeless at math....
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