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Math Help - Calc 1 question

  1. #1
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    Calc 1 question

    find the derivitive f(x) = -4/x^2 use the limit process

    Using fx=(x+Dx)-fx/Dx

    I get -4/(x+Dx)^2/x^2 + 4/x^2 and get lost in the math - am I on the right track?
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  2. #2
    Moo
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    Hello,

    Quote Originally Posted by weezie23 View Post
    find the derivitive f(x) = -4/x^2 use the limit process

    Using fx=(x+Dx)-fx/Dx

    I get -4/(x+Dx)^2/x^2 + 4/x^2 and get lost in the math - am I on the right track?



    f'(x)=\frac{f(x+Dx)-f(x)}{Dx}

    f({\color{red}x+Dx})=\frac{-4}{({\color{red}x+Dx})^2}


    ---> f'(x)=\frac{\frac{-4}{(x+Dx)^2}+\frac{4}{x^2}}{Dx}

    Did you catch your mistake ? Now, try to simplify (show your work, it'd be better)
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  3. #3
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    It's time to get UNlost. You just have to sort through it.

    1) Fix your notation:

    These are NOT the same:

    x+3/5 and (x+3)/5

    Remember your Order of Operations.

    2) Don't write things that make no sense.

    You have: fx=(x+Dx)-fx/Dx

    Notice how "fx" is on both sides. I'm sure you didn't mean that. Plus, there's and 'f' missing on the right -- f(x+Dx)?
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  4. #4
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    As far as I get is 8x^2+8xDx+4Dx^2/(x+Dx)-x^2



    Quote Originally Posted by Moo View Post
    Hello,






    f'(x)=\frac{f(x+Dx)-f(x)}{Dx}

    f({\color{red}x+Dx})=\frac{-4}{({\color{red}x+Dx})^2}


    ---> f'(x)=\frac{\frac{-4}{(x+Dx)^2}+\frac{4}{x^2}}{Dx}

    Did you catch your mistake ? Now, try to simplify (show your work, it'd be better)
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  5. #5
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    You didn't listen to me about the notation, did you?

    If you are VERY CAREFUL, you will see it. If you are sloppy, it will work only by luck.
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