1. Not finding help here? Sign up for a free 30min 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!

Finding horizontal tangents on an interval

  1. Oct 22, 2010 #1
    1. The problem statement, all variables and given/known data

    Determine all x in [-pi/2, pi/2] at which the graph has horizontal tangents.

    2. Relevant equations

    1.) f'(x)= 9cos(x)-2sin(x)
    2.) f'(x)= -5csc(x) (5cot(x)-csc(x))

    3. The attempt at a solution

    1.) 9cos(x)=2sin(x)
    9/2=sin(x)/cos(x)
    9/2=tan(x)
    and then I'm not sure what to do with 9/2?

    2.) 5cot(x)=csc(x)
    5= csc(x)/cot(x)
    5=1/cos(x)
    cos(x)=1/5
    same problem here... what do I do with 1/5?
     
  2. jcsd
  3. Oct 22, 2010 #2

    hotvette

    User Avatar
    Homework Helper

    You are looking for the values of x such that tan(x) = 9/2. Remember inverse trigonometric functions (i.e. sine / arcsine, cos / arccos, tan / arctan, etc.)?
     
  4. Oct 22, 2010 #3
    I'm sorry, I still don't know--I'm not aware of a "simple" solution to tan(x)=9/2. How would I go about finding the solution?
     
  5. Oct 22, 2010 #4
    Look up the arctan function (also called inverse tangent) and its uses.
     
  6. Oct 23, 2010 #5
    Got it. Thanks!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Finding horizontal tangents on an interval
Loading...