Results 1 to 8 of 8

Math Help - Solve system by elimination

  1. #1
    Newbie
    Joined
    Dec 2009
    Posts
    6

    Solve system by elimination

    How do you Solve a system by elimination? Please explain how you get the answer. Thanks in advance!

    Problem:
    Solve each system by elimination

    -a + b -c = -5
    6a + 5b + 2c = 9
    -3a -2b -c = -3
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member
    Joined
    Jun 2009
    From
    Africa
    Posts
    641

    Smile

    Quote Originally Posted by MajorGriffin View Post
    How do you Solve a system by elimination? Please explain how you get the answer. Thanks in advance!

    Problem:
    Solve each system by elimination

    -a + b -c = -5
    6a + 5b + 2c = 9
    -3a -2b -c = -3
    multiply the first line by 6 and add it to the second (write down what you've got) multiply it again by -3 and add it to the third (write what you've got).
    now leave the first line intact,you just used it to eliminate and write down the two lines that you've got.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Dec 2009
    Posts
    6
    Quote Originally Posted by Raoh View Post
    multiply the first line by 6 and add it to the second (write down what you've got) multiply it again by -3 and add it to the third (write what you've got).
    now leave the first line intact,you just used it to eliminate and write down the two lines that you've got.
    Okay, so.
    Multiplied the top line by 6
    Got -6a+6b-6c=-30 correct?
    added it to the second line and got
    11b-4c=-21 (the a's canceled out)
    multiplied that by -3 and got:
    -33b + 12c = 63 (Is this right so far?) Because then you say to leave the first line intact (-a + b - c = -5) and write down the two lines left would it look something like...

    -a + b - c = -5
    11b - 4c = -21
    -33b + 12c = 63

    I'm not sure what this is supposed to look like as a final answer. I just followed your instructions the best I could
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Super Member
    Joined
    Jun 2009
    From
    Africa
    Posts
    641

    Smile

    Quote Originally Posted by MajorGriffin View Post
    Okay, so.
    Multiplied the top line by 6
    Got -6a+6b-6c=-30 correct?
    added it to the second line and got
    11b-4c=-21 (the a's canceled out)
    multiplied that by -3 and got:
    -33b + 12c = 63 (Is this right so far?) Because then you say to leave the first line intact (-a + b - c = -5) and write down the two lines left would it look something like...

    -a + b - c = -5
    11b - 4c = -21
    -33b + 12c = 63

    I'm not sure what this is supposed to look like as a final answer. I just followed your instructions the best I could
    Almost but not quite.
    you should use the first line to ELIMINATE.and DON'T Touch it.
    so you multiply it by 6 to eliminate a of the second line.
    and You didn't multiply it by -3 to eliminate a of the third line.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Newbie
    Joined
    Dec 2009
    Posts
    6
    I don't understand what you mean
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Super Member
    Joined
    Jun 2009
    From
    Africa
    Posts
    641

    Smile

    Quote Originally Posted by MajorGriffin View Post
    I don't understand what you mean
    it's Gauss elimination method.
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Super Member
    Joined
    Jun 2009
    From
    Africa
    Posts
    641

    Smile

    \left\{\begin{matrix}<br />
-a+b-c=-5\\ <br />
6a+5b+2c=9\\ <br />
-3a-2b-c=-3<br />
\end{matrix}\right. \Leftrightarrow \left\{\begin{matrix}<br />
-a+b-c=-5\\ <br />
11b-4c=-21\\ <br />
-5b+2c=12<br />
\end{matrix}\right. \Leftrightarrow \left\{\begin{matrix}<br />
-a+b-c=-5\\ <br />
11b-4c=-2\\ <br />
c=\frac{12+5b}{2}<br />
\end{matrix}\right.
    now use substitution to find b.
    hope that helps.
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Newbie
    Joined
    Dec 2009
    Posts
    6
    Okay thanks for clearing that up!
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 2
    Last Post: January 11th 2012, 11:57 PM
  2. Solve a system using Gauss-Jordan elimination.
    Posted in the Advanced Algebra Forum
    Replies: 6
    Last Post: September 22nd 2011, 12:25 AM
  3. solve the system through systematic elimination...
    Posted in the Differential Equations Forum
    Replies: 6
    Last Post: March 27th 2011, 07:42 AM
  4. Guassian elimination to solve system
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: March 24th 2009, 03:31 AM
  5. Replies: 0
    Last Post: October 8th 2008, 08:58 PM

Search Tags


/mathhelpforum @mathhelpforum