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Math Help - Use the definition of Derivative to find f`(x)

  1. #1
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    Question Use the definition of Derivative to find f`(x)

    1. f(x) = 4
    (√5 - x)

    Note: 5 - x is all squared.


    2. f(x) = 2x
    x - 2


    3. f(x) =
    √x + 2
    3
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  2. #2
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    Quote Originally Posted by valeriegriff View Post
    1. f(x) = 4
    (√5 - x)

    Note: 5 - x is all squared.
    Is it all squared or all in the square root? A clearer way of writing that would be 4/√(5- x). Use parentheses!

    That is equal to 4(5- x)^{-1/2}. Use the "power rule" (derivative of x^n is n x^{n-1} and the chain rule.

    [SIZE=5]
    2. f(x) = 2x
    x - 2
    f(x)= 2x/(x- 2). Use the quotient rule!

    3. f(x) = √x + 2
    3
    (1/3)(x+2)^{1/2}

    Again, "power rule" and "chain rule".
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  3. #3
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    i understand the concept of rules. but the problem i am having with these questions is that i was asked to find the derivative using the definition. i know the definition is
    f`(x) = f( x + h) - f(x) Żall over- h

    but when i place the equations into the definition i cannot get the same answer as the rules. there is something i am doing wrong and i dont know what..

    please help..
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  4. #4
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    Quote Originally Posted by valeriegriff View Post
    i understand the concept of rules. but the problem i am having with these questions is that i was asked to find the derivative using the definition. i know the definition is
    f`(x) = f( x + h) - f(x) Żall over- h

    but when i place the equations into the definition i cannot get the same answer as the rules. there is something i am doing wrong and i dont know what..

    please help..
    Show all your work and then someone can point out what you're doing wrong.
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