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Math Help - okay, i keep getting this inverse wrong...

  1. #1
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    okay, i keep getting this inverse wrong...

    Problem:
    Let F(x) = (x+2)/(x+7)

    so what is F^(-1) (-7)= ?
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  2. #2
    A riddle wrapped in an enigma
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    Quote Originally Posted by lsnyder View Post
    Problem:
    Let F(x) = (x+2)/(x+7)

    so what is F^(-1) (-7)= ?
    Hi lsnyder,

    f(x)\Rightarrow y=\frac{x+2}{x+7}

    f^{-1}(x)\Rightarrow x=\frac{y+2}{y+7}

    Now solve for y. Use this inverse function to find f^{-1}(-7)
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  3. #3
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    i have solved for y, which i get

    y=(2-7x)/x
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  4. #4
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    Quote Originally Posted by lsnyder View Post
    i have solved for y, which i get

    y=(2-7x)/x
    Hi isnyder,

    Not what I got. Check your algebra again and see if you can come up with the correct denominator. Your numerator is fine.

    x=\frac{y+2}{y+7}

    x(y+7)=y+2

    Distribute on the left and group your y terms togther on the left. Continue from there.

    xy+7x=y+2

    xy-y=2-7x

    See? Now factor out a y on the left and then divide.
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  5. #5
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    i already did that & got

    Y=(2-7x)/x

    then if replace the x with -7, i get

    Y=(2-7(-7))/ (-7)

    Y=51/-7

    which is wrong
    ??? what do i do???
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  6. #6
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    Take your time and work on your factoring.



    y(x-1)=2-7x

    y=(2-7x)/(x-1)

    When you factor out the y the -1 still remains. So you almost had it.
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