Results 1 to 3 of 3

Math Help - Trig exact values

  1. #1
    Newbie
    Joined
    Apr 2008
    Posts
    7

    Trig exact values

    Find the exact value of sin 195 given sin 195=sin (225-30)

    Basically what I need to know is how sin 225 = -sin 45....how do I know that sin 225 is equal to -sin 45?
    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 Ericonda View Post
    Find the exact value of sin 195 given sin 195=sin (225-30)

    Basically what I need to know is how sin 225 = -sin 45....how do I know that sin 225 is equal to -sin 45?
    sin(225-30)=\sin(225)cos(30)-cos(225)sin(30)=\frac{-\sqrt{2}}{2}\frac{\sqrt{3}}{2}-\frac{-\sqrt{2}}{2}\frac{1}{2}
    you can multiply
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Moo
    Moo is offline
    A Cute Angle Moo's Avatar
    Joined
    Mar 2008
    From
    P(I'm here)=1/3, P(I'm there)=t+1/3
    Posts
    5,618
    Thanks
    6
    Quote Originally Posted by Ericonda View Post
    how do I know that sin 225 is equal to -sin 45?
    Hello,

    Because 225=180+45

    And if you look at a unit circle, sin(180+x)=-sin(x)
    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 23rd 2011, 11:50 PM
  2. Exact values using trig identities
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: April 29th 2009, 04:27 PM
  3. Trig Exact Values
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: November 3rd 2008, 02:04 PM
  4. trig functions and exact values
    Posted in the Trigonometry Forum
    Replies: 11
    Last Post: July 2nd 2008, 04:58 AM
  5. Trig identities, exact values
    Posted in the Trigonometry Forum
    Replies: 3
    Last Post: November 6th 2007, 03:50 AM

Search Tags


/mathhelpforum @mathhelpforum