Results 1 to 3 of 3

Math Help - Odd quadrant information?

  1. #1
    Newbie
    Joined
    Dec 2011
    Posts
    1

    Odd quadrant information?

    I understand that if Cosθ is say 2/3, and 0<θ<pi/2 then both x and y are positive since that limit shows the angle is in quadrant 1.

    However, in that same context, SinB is 3/5, and -pi/2<B<0 what does that mean?

    why is the pi/2 now on the left and negative? What does that do to X, Y, and R?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    -1
    e^(i*pi)'s Avatar
    Joined
    Feb 2009
    From
    West Midlands, England
    Posts
    3,053
    Thanks
    1

    Re: Odd quadrant information?

    Quote Originally Posted by Nosophoros57 View Post
    I understand that if Cosθ is say 2/3, and 0<θ<pi/2 then both x and y are positive since that limit shows the angle is in quadrant 1.

    However, in that same context, SinB is 3/5, and -pi/2<B<0 what does that mean?

    why is the pi/2 now on the left and negative? What does that do to X, Y, and R?
    Consider a triangle constructed in the unit circle with angle \theta and hypotenuse of the radius hence 1.

    From basic trig rations you know that:
    • \sin(\theta) = \frac{opp}{adj} = \frac{y}{r} = y
    • \cos(\theta) = \frac{x}{r} = x
    • \tan(\theta) = \frac{y}{x}


    Therefore the quadrant will determine the sign of x and y and hence of sin,cos and tan
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,963
    Thanks
    1784
    Awards
    1

    Re: Odd quadrant information?

    Quote Originally Posted by Nosophoros57 View Post
    I understand that if Cosθ is say 2/3, and 0<θ<pi/2 then both x and y are positive since that limit shows the angle is in quadrant 1.
    However, in that same context, SinB is 3/5, and -pi/2<B<0 what does that mean? why is the pi/2 now on the left and negative? What does that do to X, Y, and R?
    Actually you have that all wrong.
    If \cos(\theta)>0 then -\tfrac{\pi}{2}<\theta<\tfrac{\pi}{2}

    If \sin(\theta)>0 then 0<\theta<\pi
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Which Quadrant?
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: October 20th 2009, 03:02 PM
  2. Which Quadrant?
    Posted in the Algebra Forum
    Replies: 2
    Last Post: August 31st 2009, 09:07 PM
  3. Quadrant x
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: February 24th 2008, 09:31 AM
  4. first quadrant.....
    Posted in the Calculus Forum
    Replies: 2
    Last Post: May 28th 2007, 08:58 AM
  5. Which quadrant is this in?
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: June 22nd 2005, 02:47 AM

Search Tags


/mathhelpforum @mathhelpforum