Results 1 to 3 of 3

Math Help - i need trig. help.

  1. #1
    Newbie
    Joined
    Jun 2008
    Posts
    17

    i need trig. help.

    84.

    If f(x) = cox x and f(a) = 1/4, find the exact value of:
    A. f(-a)
    B. f(a) + f(a+ 2pi) + f(a-2pi)

    88.

    If f(x) csc x and f(a) = 2, find the exact value of
    A. f(-a)
    B. f(a) + f(a + 2pi) + f(a + 4pi)
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor Mathstud28's Avatar
    Joined
    Mar 2008
    From
    Pennsylvania
    Posts
    3,641
    Quote Originally Posted by desperate_on_sunday_night View Post
    84.

    If f(x) = cox x and f(a) = 1/4, find the exact value of:
    A. f(-a)
    B. f(a) + f(a+ 2pi) + f(a-2pi)

    88.

    If f(x) csc x and f(a) = 2, find the exact value of
    A. f(-a)
    B. f(a) + f(a + 2pi) + f(a + 4pi)
    I will give you some hints

    \cos(-x)=\cos(x)
    \cos(x\pm{2\pi})=\cos(x)
    Follow Math Help Forum on Facebook and Google+

  3. #3
    o_O
    o_O is offline
    Primero Espada
    o_O's Avatar
    Joined
    Mar 2008
    From
    Canada
    Posts
    1,407
    f(x) = \cos x is an even function meaning that: f(x) = f(-x). You know what f(a) is so you can certainly find f(-a).

    Also, cos x is a periodic function. If you've learned the unit circle, you can see that adding 2pi to your angle will have you end up at the exact same point on the unit circle. Same reasoning applies if you went backwards 2pi and went around the circle multiple times (i.e. multiples of 2pi). So: f(x) = f(x \pm 2k\pi) \: \: k \in \mathbb{Z} (k is an integer)

    ----------------------------------------------

    f(x) = \csc x is an odd function, i.e. f(-x) = -f(x). Use similar logic from above to arrive at your answers.

    If you still have any problems, don't hesitate to post back!
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Compute Trig Function Values, Solve Trig Equation
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: September 8th 2011, 08:00 PM
  2. Replies: 7
    Last Post: April 15th 2010, 09:12 PM
  3. Replies: 6
    Last Post: November 20th 2009, 05:27 PM
  4. Replies: 1
    Last Post: July 24th 2009, 03:29 AM
  5. Trig Equations with Multiple Trig Functions cont.
    Posted in the Trigonometry Forum
    Replies: 4
    Last Post: April 7th 2008, 06:50 PM

Search Tags


/mathhelpforum @mathhelpforum