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!

Trig Problem, Help please.

  1. Oct 18, 2013 #1
    1. The problem statement, all variables and given/known data

    Simplify cot(θ)sin(-θ) so that it is a single trig function of positive θ

    2. Relevant equations


    3. The attempt at a solution
    I changed cot(θ) to
    cos(θ)/sin(θ) X Sin(-θ)/1

    I stated that sin(-θ) and sin(θ) were the same and then cancled out the sin(θ) and sin (-θ) to get cos(θ)/1 or Cos(θ)


    I feel like this is right but I only got half the points I was supposed to get, not quite sure what I did wrong.
     
  2. jcsd
  3. Oct 18, 2013 #2

    berkeman

    User Avatar

    Staff: Mentor

    sin(-θ) and sin(θ) are not quite the same. What is different about them?
     
  4. Oct 18, 2013 #3
    The degree angle is negative in one of them, which would give you a value between 0 and negative one? I just cant seem to grasp how to simplify this.
     
  5. Oct 18, 2013 #4

    berkeman

    User Avatar

    Staff: Mentor

    Is the sin() function even or odd? Look at a plot of sin(x) over -360 degrees to +360 degrees. What does it do around x=0?
     
  6. Oct 18, 2013 #5
    Wait this would then give me
    cosθ/sinθ X -sinθ/1
    yeah?
    Or...maybe I am on the wrong track...
     
  7. Oct 18, 2013 #6

    berkeman

    User Avatar

    Staff: Mentor

    :smile: So do you see why you only got partial points?
     
  8. Oct 18, 2013 #7
    Sin is a odd function, though I do not understand why. Or what that quite means, I just found it in my notes. except maybe it is opposite of it such as it is the same value except with a negative sign on it.
     
  9. Oct 18, 2013 #8
    Ok well if this is right then the sinθ would cancel out and wouldn't the negative still be there? As in it would then simplify to -cosθ which is not what it asked for. It asked that "so that it is a single trig function of positive θ "
     
  10. Oct 18, 2013 #9

    berkeman

    User Avatar

    Staff: Mentor

    For odd functions, f(-x) = -f(x). For even functions, f(-x) = f(x). Can you see how sin() is an odd function, and cos() is an even function?

    The question is asking for the answer to be expressed in terms of positive θ. -cos(θ) is a function of positive θ.
     
  11. Oct 18, 2013 #10
    OH!!!! Thank you so very much, yes that makes lots of sense to me. Alright, thank you.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Trig Problem, Help please.
Loading...