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What are the first and second derivatives of the function

  1. Dec 16, 2003 #1
    What are the first and second derivatives of the function

    f(x)=(3-x)/(2x+5)

    How do i find them, do i use the quotient rule or do i change it to

    f(x)=(3-x)*(2x+5)^-1 and use the product rule?
     
  2. jcsd
  3. Dec 16, 2003 #2
    Personally I like the product rule better, but you get the same answer either way, so use whichever one you prefer.
     
  4. Dec 16, 2003 #3
    I think i got it

    f'(x)= -11(2x+5)^-2
    f''(x)= 44(2x+5)^-3

    but does anyone know of a web site where i can type in the function and it will show me all the max, mins, asymptotes, holes, cusps ...
     
  5. Dec 16, 2003 #4
    You made a mistake when you combined your terms in the first deriv., & therefore the 2nd is wrong too.
     
  6. Dec 16, 2003 #5
    You haven't applied the Product Rule properly

    http://www.math.temple.edu/~cow/
     
  7. Dec 17, 2003 #6
    How are roy's answers incorrect?

    f'(x)= -11(2x+5)^-2
    f''(x)= 44(2x+5)^-3

    -11 times the quantity (2x+5) to the power of -2 is the correct answer as seen HERE:

    roy's answer could be written:

    f'(x)= -11/(2x+5)^2
    f''(x)= 44/(2x+5)^3

    and it would be equivalent to what he has above.
     
  8. Dec 17, 2003 #7
    Sorry those are not incorrect
     
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