Results 1 to 3 of 3

Math Help - Trigonomatric Identities

  1. #1
    Junior Member
    Joined
    Jun 2010
    Posts
    35

    Trigonomatric Identities

    a. Find the exact value of sin 180 by using sin (270 90 )


    b. Find the exact value of sin 150 by using sin (210 60 )

    c. Use the value of sin 150 found in b to find sin (15 ) by using sin
    (150 165 )
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Senior Member
    Joined
    Jul 2010
    From
    Vancouver
    Posts
    432
    Thanks
    16
    For part a) you need to use the summation formula for the sine function. You have to recognize that sin(270) = -Sin(90) = -1 and cos(270) = cos(90) = 0.

    Then you have
    <br />
\sin(270-90) = \sin(270)\cos(90) - \sin(90)\cos(270) = (-1)(0) - (1)(0) = 0

    This should not be surprising since 270-90 = 180 and we know that the sine function is zero there. It is a very similar situation in b) and c) and you should be able to do it yourself. Try it out and if you can't do it, show your work and ask for help!
    Follow Math Help Forum on Facebook and Google+

  3. #3
    A riddle wrapped in an enigma
    masters's Avatar
    Joined
    Jan 2008
    From
    Big Stone Gap, Virginia
    Posts
    2,551
    Thanks
    12
    Awards
    1
    Quote Originally Posted by soni View Post

    b. Find the exact value of sin 150 by using sin (210 60 )


    Hi soni,

    \sin(u \pm v)=\sin u \cos v \pm \cos u \sin v

    \sin(210-60)=\sin 210 \cos 60-\cos 210 \sin 60=\left(-\frac{1}{2}\right)\left(\frac{1}{2}\right)-\left(-\frac{\sqrt{3}}{2}\right)\left(\frac{\sqrt{3}}{2}\  right)=.5

    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 6
    Last Post: June 22nd 2010, 11:59 PM
  2. identities..
    Posted in the Trigonometry Forum
    Replies: 3
    Last Post: July 29th 2009, 12:33 PM
  3. Identities
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: July 14th 2009, 07:58 AM
  4. identities
    Posted in the Trigonometry Forum
    Replies: 5
    Last Post: November 2nd 2008, 03:34 PM
  5. Identities
    Posted in the Trigonometry Forum
    Replies: 3
    Last Post: July 11th 2008, 03:53 AM

Search Tags


/mathhelpforum @mathhelpforum