Results 1 to 6 of 6

Math Help - Trig Exreme Values

  1. #1
    Member
    Joined
    Sep 2009
    Posts
    78

    Trig Exreme Values

    Determine the extreme values of the following function in the given interval.

    f(x)=2sin4x+3 , XE [0, pi]

    This is my work:

    f'(x)=2cos4x (4)
    f'(x)=8cos4x

    Now I am trying to find the critical numbers, but I'm not sure how to solve for x.

    f'(x)=0
    cos4x=0
    x=22.5

    Is this right?
    Last edited by john-1; November 7th 2009 at 05:19 PM.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Senior Member
    Joined
    Dec 2008
    Posts
    319
    Remember that when k is a constant, \frac{d}{dx}(k)=0. Other than that, you are on the right track.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Sep 2009
    Posts
    78
    EDIT:::::::::

    I'm not getting correct answer with abs min with the back of my textbook.

    I get f(0) = 3
    and f(pi) = 3
    f(22.5)=5

    Therefore the max is 5 and the min is 3. The back of the book has min as 1. How did they get this?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    No one in Particular VonNemo19's Avatar
    Joined
    Apr 2009
    From
    Detroit, MI
    Posts
    1,823
    Quote Originally Posted by john-1 View Post
    EDIT:::::::::

    I'm not getting correct answer with abs min with the back of my textbook.

    I get f(0) = 3
    and f(pi) = 3
    f(22.5)=5

    Therefore the max is 5 and the min is 3. The back of the book has min as 1. How did they get this?
    \cos{x}=0 when n\frac{\pi}{2} with n odd.

    Therefore

    \cos(4x)=0\Rightarrow{x}=n\frac{\pi}{8}, n odd.

    Now considering the given interval...
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Member
    Joined
    Sep 2009
    Posts
    78
    Yes I know, Thank you, but I am asking about the abs min.
    How did they get 1?

    I get f(0) = 3
    and f(pi) = 3
    f(22.5)=5

    Therefore the max is 5 and the min is 3. The back of the book has min as 1.
    Follow Math Help Forum on Facebook and Google+

  6. #6
    No one in Particular VonNemo19's Avatar
    Joined
    Apr 2009
    From
    Detroit, MI
    Posts
    1,823
    Take a look at the graph.

    f(\frac{\pi}{8})=5

    f(\frac{3\pi}{8})=1 and etc...

    The endpoints are therefore irrelevant.
    Last edited by VonNemo19; January 18th 2010 at 11:43 AM.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. trig exact values
    Posted in the Trigonometry Forum
    Replies: 3
    Last Post: September 24th 2011, 12:50 AM
  2. Compute Trig Function Values, Solve Trig Equation
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: September 8th 2011, 08:00 PM
  3. trig values
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: February 24th 2010, 12:19 AM
  4. trig max/min values
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: November 23rd 2009, 01:30 PM
  5. help with hw-trig functions and values
    Posted in the Trigonometry Forum
    Replies: 4
    Last Post: September 24th 2007, 07:28 PM

Search Tags


/mathhelpforum @mathhelpforum