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!

Solving Trigonometric Equations

  1. Apr 5, 2007 #1
    1. The problem statement, all variables and given/known data
    use the inverse functions where necessary to find all solution of the equation in the interval [0,2pi). Use a graphing utility to verify.


    2. Relevant equations

    3. The attempt at a solution

    The answer is pi/2 and 3pi/2 from my teacher..

    stuck :confused:
  2. jcsd
  3. Apr 5, 2007 #2
    You can solve it like any other quadratic. What would you do with 2y2 + 3y = 0 ?
  4. Apr 6, 2007 #3


    User Avatar
    Homework Helper

    also remember you cannot divide both side by cos x (or y in turdferguson redefinition), because cos x can be zero (and in fact it is a solution)
  5. Apr 6, 2007 #4


    User Avatar
    Science Advisor
    Homework Helper

    As turdferguson points out, it's not completely valid to divide both sides by cos(x). What if cos(x)=0?
  6. Apr 6, 2007 #5
    I can factor out cosx? (sorry, this is midterm, and this stuff is what we did in January:p)

    cosx=0 and cosx=-3/2

    I can figure cosx=0 to be x=pi/2 and 3pi/2 but can anyone remind me why cosx=-3/2 doesn't work (invalid in calc)?
    I think because adj/hyp, and adj has to be smaller than hyp, so cos or sin > 1 = no solution?
  7. Apr 6, 2007 #6


    User Avatar
    Science Advisor
    Homework Helper

    Yes, that's the reason.
  8. Apr 6, 2007 #7


    User Avatar
    Staff Emeritus
    Science Advisor

    No real number solution. It is possible to have a complex value that has cosine equal to 1.5.
  9. Apr 6, 2007 #8
    Could you also look at it this way? f(x)=2cox(x)+3 -- It's going to be translated? up 3 units and is only has an amplitude of 2 so it will never cross the x-axis, so there are not any x-intercepts.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Solving Trigonometric Equations