1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Arithmetic Question for Finding Derivative using Quotient Rule

  1. Jul 3, 2011 #1
    1. The problem statement, all variables and given/known data

    Find dy/dx for the following function:

    y = (11-cos(x))/(2+cos(x))

    2. Relevant equations

    Quotient Rule:

    y'= ((g(x))(f'(x)) - (f(x))(g'(x)))/ (g(x)^2)

    3. The attempt at a solution

    I used the quotient rule to come up with this:

    y'= ((2+cos(x))(sin(x)) - (11-cos(x))(-sin(x))) / ((2+cos(x))^2)

    Now, the trouble that I am having is simplifying this.

    The final answer should turn out to be :


    I am overlooking some basic arithmetic here, but I can't seem to find out what I am missing. Am I supposed to multiply out the expressions first and then combine like terms? Basically, how do I go from the expanded version to the simplified version? Thank you
  2. jcsd
  3. Jul 3, 2011 #2


    User Avatar
    Gold Member

    Yes try expanding it; simplifying it to the required expression is just a matter of collecting like terms
  4. Jul 3, 2011 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Your denominator looks to be in the same form as the desired answer.

    Play around with the numerator.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Arithmetic Question for Finding Derivative using Quotient Rule