Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Average rate of change

  1. Feb 20, 2012 #1
    1. The problem statement, all variables and given/known data

    Consider the graph of the function f(x) = 5x^2 - 8x

    Determine the average rate of change as x changes from -1 to 4

    3. The attempt at a solution

    f(4) - f(-1) / 4 - 1

    The answer is not correct according to the answer sheet. :(
  2. jcsd
  3. Feb 20, 2012 #2


    User Avatar
    Science Advisor
    Homework Helper

    Shouldn't your denominator be 4-(-1)?
  4. Feb 20, 2012 #3


    Thank you. Such a stupid mistake.
  5. Feb 20, 2012 #4


    Staff: Mentor

    In addition to what Dick said, you need more parentheses when you write out expressions like that in plain text.

    This would be interpreted as f(4) - [itex]\frac{f(-1)}{4}[/itex] - 1
    If you write it on a single line, do it like this: (f(4) - f(-1))/(4 - (-1)).
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook