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!

Homework Help: How to graph a sin function with respect to it's limits and x intercepts

  1. Mar 28, 2012 #1
    I have been given a question to sketch the curve of y=sin(x). I have looked into finding the domain which I understand but I don't understand how I prove the x intercepts mathematically as when I make x=0 I obviously get a 0 value for y but a sin curve obviously intercepts and pi and 2pi etc, how do I prove this ? Also why when I put sin(3pi/2) into the calculator do I not get a negative figure ? or why when I put pi and 2pi in do I not get zero ?
  2. jcsd
  3. Mar 28, 2012 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Check that your calculator is in radian mode, not degree mode.
  4. Mar 28, 2012 #3
    sorry, i didn't have my calculator in radian mode. Still I don't understand how I get the values of the x intercepts mathamatically in the same way as you do with polynomial expressions ?
  5. Mar 28, 2012 #4
    It's actually part what periodic functions are.
    for a periodic function g(x): g(x+P)=g(x) where P is the period.
    So your function [itex] f(x)=sin(x) [/itex] is as good as [itex] f(x)=sin (x \pm n\pi) [/itex] n=0,1,2....
    so [itex] x=sin^{-1}(y) \pm n\pi [/itex]
    now go ahead and put y=0 to get all your x intercepts.
  6. Mar 28, 2012 #5
    that's the key to the door, thankyou :)
  7. Mar 31, 2012 #6
    I've been trying all week but what I can't understand is that as [sin][/-1](0) is always 0 then any value I put in between 0 and 2∏ I get that value as an x intercept, where am I getting confused ?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook