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Math Help - [SOLVED] Solving sim equations.

  1. #1
    ADY
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    [SOLVED] Solving sim equations.

    I need some real help with this please guys, ok so here's the example given to me from tutor:

    Example 2x + y = 1, x + 3y = -7


    Method 1 - add/subtract


    2x + y = 1
    x - 3y = 11

    You can add or subtract. Adding will enable you to focus on x, subtracting will focus on y.

    Perhaps the easiest is to add. BUT first of all you must scale the first expression by 3 to enable the yís to match, giving the zero count for y, you require.


    So 6x + 3y = 3 (Note each part has been x 3)
    x - 3y = 11

    Adding 7x = 14 (Note the zero count for y - this is what you x = 2 want to happen)


    Substituting back into one of the previous expressions -

    2(2) + y = 1, 4 + y = 1, y = -3

    ANSWER x = 2, y = -3

    My first problem is, from the example equations, how can it be re-arranged and make 11?!

    I'm confused with this topic, thanks

    ADY
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    i think you got the right answer but what do you mean by this?
    My first problem is, from the example equations, how can it be re-arranged and make 11?!
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  3. #3
    ADY
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    Its not my answer, its an example.

    and i need to understand the methodology of it as i dont get it at all, with reference to the first line, where's " 11" come from?
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    Talking

    2x + y = 1
    x - 3y = 11

    i call it elimination method

    you can do that like this way. subtract the first from the second and get x.

    x-3y=11

    \frac{-2x-y=-1}{-x-4y=10}


    -x=10+4y

    x=-10-4y

    now you have x
    then use substitution method: you can use either 1st or second equation

    x-3y=11

    (-10-4y)-3y=11


    -7y=11+10

    -7y=21

    y=-3

    substitute y to get x

    x-3y=11

    x-3(-3)=11

    x+9=11

    x=11-9

    x=2

    now you have the value of both variables then substitute to check:

    x=2

    y=-3

    B. x-3y=11

    2-3(-3)=11

    2+9=11

    11=11

    A. 2x +y = 1

    2(2)+(-3)=1

    4-3=1

    1=1

    Note:11 is just the answer on the equation you are solving but there is no value of x and y so you need to find their values.
    Last edited by princess_21; February 10th 2009 at 07:28 AM.
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  5. #5
    ADY
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    ok but the example is

    Example

    2x + y = 1
    x + 3y = -7

    So where did you get 11 from?
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  6. #6
    ADY
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    ok, i think im there.

    so how would you solve

    y=22x + 100, y=25x + 10
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  7. #7
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    Quote Originally Posted by ADY View Post
    I need some real help with this please guys, ok so here's the example given to me from tutor:

    Example 2x + y = 1, x + 3y = -7


    Method 1 - add/subtract


    2x + y = 1
    x - 3y = 11 <====Don't know where this came from!


    My first problem is, from the example equations, how can it be re-arranged and make 11?!

    I'm confused with this topic, thanks

    ADY
    Quote Originally Posted by ADY View Post
    ok but the example is

    Example

    2x + y = 1
    x + 3y = -7

    So where did you get 11 from?
    Hi ADY,

    Your second equation x + 3y = -7 cannot be derived from x - 3y = 11. You've either miscopied the example or there's a misprint somewhere.
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  8. #8
    A riddle wrapped in an enigma
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    Quote Originally Posted by ADY View Post
    ok, i think im there.

    so how would you solve

    y=22x + 100, y=25x + 10
    Hi ADY,

    Since y = y , you can equate the right side of the equations as well.

    22x+100=25x+10

    Solve for x. Then substitute the value for x back into either original equation to find y.
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  9. #9
    ADY
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    Quote Originally Posted by masters View Post
    Hi ADY,

    Your second equation x + 3y = -7 cannot be derived from x - 3y = 11. You've either miscopied the example or there's a misprint somewhere.

    Thanks the original equation was:

    2x + y = 1
    x + 3y + -7

    Can that work?
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  10. #10
    ADY
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    Quote Originally Posted by masters View Post
    Hi ADY,

    Since y = y , you can equate the right side of the equations as well.

    22x+100=25x+10

    Solve for x. Then substitute the value for x back into either original equation to find y.
    Can i have further help with this please, i dont know where im even starting
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  11. #11
    A riddle wrapped in an enigma
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    Quote Originally Posted by masters View Post
    Hi ADY,

    Since y = y , you can equate the right side of the equations as well.

    22x+100=25x+10

    Solve for x. Then substitute the value for x back into either original equation to find y.
    Ok ADY,

    22x+100=25x+10

    First subtract 22x from both sides:

    100=3x+10

    Next, subtract 10 from both sides:

    90=3x

    Finally, divide by 3:

    30=x

    Now, substitute 30 back into y = 22x + 100 to get y = 22(30) + 100, and y = 760
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    Quote Originally Posted by ADY View Post
    ok, i think im there.

    so how would you solve

    y=22x + 100, y=25x + 10

    so that's what you are asking I didn't realized that the two equations are different one is 7 and one is 11. you can't changed the answer. i'm sorry i didn't look at the first equation. i only saw the one with 11 as the answer.
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  13. #13
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    Quote Originally Posted by ADY View Post
    Can i have further help with this please, i dont know where im even starting
    just like what masters said equate the solution

    y=22x+100

    y=25x+10

    since y=y it's reflective propery

    22x+100=25x+10

    100-10=25x-22x

    90=3x

    30=x

    to find y, substitute x.

    y=22(30)+100

    y=660+100

    y=760

    25(30)+10

    y=750+10

    y=760

    is that what you are asking?
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  14. #14
    ADY
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    Princess - thank you!
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    A riddle wrapped in an enigma
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    Quote Originally Posted by ADY View Post
    Princess - thank you!
    I'd bet that if my name were "Precious", you'd thank me too!
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