1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    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!

Solve a Trig Equation Containing secant

  1. Nov 13, 2013 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution

    I turned it into 1/cos(5x)=5 x=θ/5
    then i switched it to cos(5x)=/1/5

    Then cos-1(1/5)=θ which = 1.36 (one solution) then divided by 5 which is .2738 which works as one solution
    since the positive cos is in the 1st and 4th quadrant i need to subtract 2pi to 1.36= 4.91 then divide by 5 which gives me .9827 which also works

    But i am stuck after that
    Last edited: Nov 13, 2013
  2. jcsd
  3. Nov 13, 2013 #2


    Staff: Mentor

    And lost your equation.

    You're making this harder than it needs to be. If 1/cos(5x) = 5, then cos(5x) = 1/5.

    You could also say that cos(5x + k*2##\pi##) = 1/5, and since cosine is positive in Q IV, you could also say that cos(-5x + k*2##\pi##) = 1/5, where k is an integer.

    Now you can take cos-1 of both sides.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted