Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Solving trig function (possible error in solutions)

  1. Nov 18, 2011 #1
    1. The problem statement, all variables and given/known data
    Alright, so I am going through the solutions to one problem that has me stumped, and initial instinct tells me it is wrong, however, I figured I would get clarification.

    3. The attempt at a solution
    [tex]2t=\pi{/}4, 5\pi{/}4[/tex]

    However, the book states both positive and negative values, rather than just positive. It's either not correct, or not clicking. tan(-π/4)=-1, not 1..
  2. jcsd
  3. Nov 18, 2011 #2

    I like Serena

    User Avatar
    Homework Helper

    What is tan(-3pi/4)?
  4. Nov 18, 2011 #3


    User Avatar
    Homework Helper

    Since your text is suggesting that there are positive and negative solutions, you are not restricted to the "principal circle" , [itex] 0 ≤ t < 2{\pi} [/itex] . So you can "go around the circle" as many times as you like:

    [tex] 2t = \frac{\pi}{4} + k \cdot 2{\pi} , \frac{5\pi}{4} + k \cdot 2{\pi} , [/tex]

    with k being any integer.
  5. Nov 19, 2011 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Are you sure the problem isn't, [itex]\sin^2(t)=\cos^2(t)\,?[/itex]
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook