Results 1 to 2 of 2

Math Help - Where have I gone wrong: Definite integrals involving trig functions

  1. #1
    Newbie
    Joined
    Jan 2010
    Posts
    10

    [pls ignore] Where have I gone wrong: Definite integrals involving trig functions

    EDIT: Let this be a warning to anyone relying on a calculator. I should have trusted myself. I entered the range in the opposite way to the calculator giving a negative solution.


    Hi All,

    Have a homework question here:
    \int^{3\pi}_{2\pi} Sin(x/4)\,dx

    I can get out:
    (-4cos(3\pi/4)) - (-4cos(2\pi/4))

    but this equals for me positive 2.8... When looking at the graph (and the solve on the calc) shouldn't it be negative? Where have I gone astray? (I think the second part of that is 0 so I assume I am doing somethign wrong in the first part).

    Cheers,

    J
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Senior Member Educated's Avatar
    Joined
    Aug 2010
    From
    New Zealand
    Posts
    433
    Thanks
    12

    Re: Where have I gone wrong: Definite integrals involving trig functions

    You haven't gone wrong anywhere, your answer of 2.8... is correct.

    What graph are you looking at the would suggest an area under the x-axis?
    Wolfram|Alpha Graph of sin(x/4)

    Did you put brackets in the right place when typing it into your calculator? Did you have your calculator in radians mode?
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. [SOLVED] Integrals Involving Powers of Trig Functions.
    Posted in the Calculus Forum
    Replies: 2
    Last Post: October 28th 2010, 01:26 AM
  2. Strange question involving definite integrals
    Posted in the Calculus Forum
    Replies: 11
    Last Post: April 9th 2010, 01:34 PM
  3. Replies: 8
    Last Post: January 28th 2010, 01:12 PM
  4. Integrals Involving Inverse Trig Functions
    Posted in the Calculus Forum
    Replies: 2
    Last Post: September 12th 2009, 10:51 PM
  5. Proof needed for an inequality involving definite integrals
    Posted in the Advanced Math Topics Forum
    Replies: 0
    Last Post: February 10th 2009, 11:00 AM

Search Tags


/mathhelpforum @mathhelpforum