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Math Help - Solve for two Variables using substitution

  1. #1
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    Solve for two Variables using substitution-Help

    I have been working on homework and cant seem to grasp the right order or equation movements in.

    AN example of a question would be

    SOlve for both FB and FA using substitution

    Given:

    -FA cos(35) + FB cos(75)=0
    -FA sin(35) +FB sin(75)= 235.4

    Any help would be appreciated

    THis is my work

    -FA cos(35) +FBcos(75)=0
    FB=FAcos(35)/cos(75)
    substitute
    -FAsin(35)+(FAcos(35)/cos(75))sin(75)=235.4

    and then whatever i try seems to make no sense after that. I may be missing a rule or something but if any have explanations that would be awesome.
    Last edited by gramgilb; September 13th 2012 at 06:45 AM.
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  2. #2
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    Re: Solve for two Variables using substitution-Help

    Quote Originally Posted by gramgilb View Post
    -FA cos(35) + FB cos(75) = 0
    -FA sin(35) + FB sin(75) = 235.4
    U = FA, V = FB
    a = cos(35), b = cos(75)
    c = sin(35), d = sin(75)

    -Ua + Vb = 0 [1]
    -Uc + Vd = 235.4 [2]

    [1]: V = Ua / b ; substitute:
    [2]: -Uc + Uad / b = 235.4
    Multiply by b:
    Uad - Ubc = 235.4b
    U(ad - bc) = 235.4b

    U = 235.4b / (ad - bc)

    Can you wrapper up now?
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  3. #3
    Senior Member MaxJasper's Avatar
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    Lightbulb Re: Solve for two Variables using substitution-Help

    Fa=
    Fb=
    Last edited by MaxJasper; September 13th 2012 at 09:21 AM.
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  4. #4
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    Re: Solve for two Variables using substitution-Help

    kk i understand now i was only multiplying b to the other side thanks for the help
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  5. #5
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    Re: Solve for two Variables using substitution-Help

    Quote Originally Posted by gramgilb View Post
    kk i understand now i was only multiplying b to the other side thanks for the help
    Well, betya you'll never do that again!
    So you should get:
    U = FA = 94.78403....
    V = FB = 299.98772...
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