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Math Help - 2 Methods

  1. #1
    Senior Member vaironxxrd's Avatar
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    2 Methods

    Hello forum Vaironl here, I have to solve some equations using two methods.
    1 Substitute x and then solve for y.
    2 Solve for y and then substitute x.

    Here is my first problem I can do the first method but I don't understand exactly how to solve the second method.
    \4x+& 9y& =30& ; x=3
    For the first method I got

    12+9y=30 =
    9y=18 =
    y= 2
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  2. #2
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    e^(i*pi)'s Avatar
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    Re: 2 Methods

    Quote Originally Posted by vaironxxrd View Post
    Hello forum Vaironl here, I have to solve some equations using two methods.
    1 Substitute x and then solve for y.
    2 Solve for y and then substitute x.

    Here is my first problem I can do the first method but I don't understand exactly how to solve the second method.
    \4x& 9y& =30& ; x=3
    For the first method I got

    12+9y=30 =
    9y=18 =
    y= 2
    4x9y = 36xy

    Is the equation meant to read 4x+9y =30\ ,\ x=3 per chance?
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  3. #3
    Senior Member vaironxxrd's Avatar
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    Re: 2 Methods

    Quote Originally Posted by e^(i*pi) View Post
    4x9y = 36xy

    Is the equation meant to read 4x+9y =30\ ,\ x=3 per chance?
    Yes sorry for the incorrect symbols
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  4. #4
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    e^(i*pi)'s Avatar
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    Re: 2 Methods

    Quote Originally Posted by vaironxxrd View Post
    Yes sorry for the incorrect symbols
    In that case solve the equation again using the value of y=2 that you just obtained to get x (x should be 3)
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  5. #5
    Senior Member vaironxxrd's Avatar
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    Re: 2 Methods

    Quote Originally Posted by e^(i*pi) View Post
    In that case solve the equation again using the value of y=2 that you just obtained to get x (x should be 3)
    Wow. I can't believe it was that simple.

    \4*x&+ 9y& = 30
    \4x& + 9*2&=30
    \4x& + 18& =30
    \4x& =12
    x& = 3
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  6. #6
    Senior Member vaironxxrd's Avatar
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    Re: 2 Methods

    Quote Originally Posted by e^(i*pi) View Post
    In that case solve the equation again using the value of y=2 that you just obtained to get x (x should be 3)
    Sorry to bother you e^(i*pi) ,
    but after spending sometime yesterday doing my homework I notice that you would solve for x first without entering y and then finding the value of y.
    Do you know how could I do that by any chance?
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  7. #7
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    e^(i*pi)'s Avatar
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    Re: 2 Methods

    Quote Originally Posted by vaironxxrd View Post
    Sorry to bother you e^(i*pi) ,
    but after spending sometime yesterday doing my homework I notice that you would solve for x first without entering y and then finding the value of y.
    Do you know how could I do that by any chance?
    Normally you would but you cannot in this case because you're told the value of x and since you only have one equation with two unknowns you can't solve simultaneously either.
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