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Math Help - couple of function problems

  1. #1
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    Given the function f(x)=2x^(5/2) :


    Calculate exactly the value(s) of x when f(x)=6. If there is more than one such value, enter all possible values as a comma separated list of exact values. x=

    If g(x)= 1/(t+7)-9
    Solve g(t)=0. If there is more than one solution, enter all solutions as a comma separated list of exact values.

    Whatever it is I'm doing is giving me the wrong answer
    So how to I go about this problem?


    My working:

    6= 2x^(5/2) is what is given for the first part, now how to i ISOLATE the x on the right side

    -------------------------------------------------------

    0= 1/(t+7) -9

    I would add 9
    9=1/(t+7) then would I multiply both sides by (t+7)
    Last edited by mr fantastic; September 22nd 2009 at 09:46 PM. Reason: Merged posts and editing for clarification
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  2. #2
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    Quote Originally Posted by midnightwynter View Post
    [snip]
    0= 1/(t+7) -9

    I would add 9
    9=1/(t+7) then would I multiply both sides by (t+7)
    Yes. Then expand and make t the subject.
    Last edited by mr fantastic; September 22nd 2009 at 10:47 PM. Reason: Tidying up the thread
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  3. #3
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    Quote Originally Posted by midnightwynter View Post
    Given the function f(x)=2x^(5/2) :
    Calculate exactly the value(s) of x when f(x)=6. If there is more than one such value, enter all possible values as a comma separated list of exact values.

    [snip]
    My working:

    6= 2x^(5/2) is what is given for the first part, now how to i ISOLATE the x on the right side

    [snip]
    Just take both sides to the power of \frac{2}{5}:

    6 = (2x)^{\frac{5}{2}}

    6^{\frac{2}{5}} = 2x

    \sqrt[5]{36} = 2x

    x = \frac{\sqrt[5]{36}}{2}.
    Last edited by mr fantastic; September 22nd 2009 at 10:50 PM. Reason: Tidying up the thread.
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