Results 1 to 3 of 3

Math Help - Radians and surds

  1. #1
    Newbie
    Joined
    Jul 2006
    Posts
    4

    Radians and surds

    Having problems with working out surds from radians. Does anyone now the whereabouts on the net where there is an extensive chart? At the moment i am struggling with cos(5*pi/6).
    Cheers in advance
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Global Moderator

    Joined
    Nov 2005
    From
    New York City
    Posts
    10,616
    Thanks
    10
    Quote Originally Posted by kendon
    Having problems with working out surds from radians. Does anyone now the whereabouts on the net where there is an extensive chart? At the moment i am struggling with cos(5*pi/6).
    Cheers in advance
    You got a calculator? Good.

    Your problem is this, you need a way to express trigonometric functions of certain angles in radical form. I remember when I was in 11th grade my cl*** was going insane with this so I have a trick which you can do.
    For example,
    \cos \frac{5\pi}{6}=-0.86602541
    Now, if you end up with a long decimal square,
    (-0.86602541)^2=.75
    But,
    .75=\frac{3}{4}
    Now, that the square root back.
    \sqrt{\frac{3}{4}}=\frac{\sqrt{3}}{2}
    Important. When you square the sign always goes away. Therefore, if you had a sign in the beginning (and you did) when you need to attach a sign here.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Grand Panjandrum
    Joined
    Nov 2005
    From
    someplace
    Posts
    14,972
    Thanks
    4
    Quote Originally Posted by kendon
    Having problems with working out surds from radians. Does anyone now the whereabouts on the net where there is an extensive chart? At the moment i am struggling with cos(5*pi/6).
    Cheers in advance
    An angle of 5 \pi/6=-\pi/6, now \pi/6 is 30 degrees, and so its cosine is \sqrt{3}/2 (consider the sides
    of half of an equilateral triangle), and the cosine function is even so

    \cos(5 \pi/6)=\cos(-\pi/6)=\cos(\pi/6)=\sqrt{3}/2

    RonL
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. [SOLVED] sec (-1/2) in radians?
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: August 26th 2011, 03:11 PM
  2. Radians help
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: March 23rd 2011, 02:51 AM
  3. Radians
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: November 23rd 2009, 02:39 AM
  4. Radians :) help please!
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: April 9th 2008, 09:59 AM
  5. Radians
    Posted in the Trigonometry Forum
    Replies: 3
    Last Post: February 21st 2008, 05:37 PM

Search Tags


/mathhelpforum @mathhelpforum