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Math Help - Simultaneous equations

  1. #1
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    Simultaneous equations

    After some much apreciated help on here by several people i would like to display this question complete with working out and soloution, could people please pick up on any mistakes i may have made

    Many Thanks

    Question 2

    2x + y = -1
    x + 2y = 4

    Multiply the first equation by 2

    Thus gives 4x + 2y = -2

    Multiply the second equation by 4

    Thus gives 4x + 8y = 16

    Now subtract equation 2 from equation 1

    Thus 0 + -6y = -18

    Thus y = 3

    Enter the value for y back into the first equation which gives…

    2x + 3 = -1

    Thus x must equal -2

    The solutions are..

    Y= 3
    X= -2
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  2. #2
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    Quote Originally Posted by duckegg911 View Post
    After some much apreciated help on here by several people i would like to display this question complete with working out and soloution, could people please pick up on any mistakes i may have made

    Many Thanks

    Question 2

    2x + y = -1
    x + 2y = 4

    Multiply the first equation by 2

    Thus gives 4x + 2y = -2

    Multiply the second equation by 4

    Thus gives 4x + 8y = 16

    Now subtract equation 2 from equation 1

    Thus 0 + -6y = -18

    Thus y = 3

    Enter the value for y back into the first equation which gives…

    2x + 3 = -1

    Thus x must equal -2

    The solutions are..

    Y= 3
    X= -2
    Your working has no error and your answer is correct. Your gold star is in the mail.

    I would however make two suggestions:

    1. Check your final answer by substituting it into the given equations.

    2. Multiplying the first equation by 2 and the second by 4 to eliminate x is a bit inefficient. I'd suggest just multiplying the second by 2 .... you'll achieve the same result with less work and therefore more quickly and with less chance of error:

    Quote Originally Posted by duckegg but edited (in red) by Mr F
    [snip]
    2x + y = -1
    x + 2y = 4

    [snip]

    Multiply the second equation by 2

    Thus gives 2x + 4y = 8

    Now subtract equation 1 from equation 2

    Thus 0 + 3y = 8 - -1 = 9

    Thus y = 3
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