Results 1 to 5 of 5

Math Help - Trigonometric Functions

  1. #1
    Newbie
    Joined
    Jul 2013
    From
    Canada
    Posts
    2

    Trigonometric Functions

    1. Determine 2 positive and 2 negative co-terminal angles for a related acute angle of 20 in quadrant III.
    2. Using the CAST rule, state the sign of each of the following:
      • sin 220
      • cos 320
      • tan 112

    3. Determine θ if cos θ = 1/2 and θ is an angle in quadrant IV.
    4. The CAST Rule describes for a quadrant which ratios have positive values. Describe why the tangent ratio is positive only in quadrants I and III.
    5. Given a point on the x-y plane, explain how you would determine a principal angle that would correspond to a terminal arm containing that point.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Sep 2012
    From
    Australia
    Posts
    3,607
    Thanks
    591

    Re: Trigonometric Functions

    Hey dvoon99.

    Can you show us what you have tried and any attempts (even partial)?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Jul 2013
    From
    Canada
    Posts
    2

    Re: Trigonometric Functions

    I honestly have no idea what to do with this... so honestly nothing has been attempted as i am not sure what to do.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor
    Joined
    Sep 2012
    From
    Australia
    Posts
    3,607
    Thanks
    591

    Re: Trigonometric Functions

    To start you off, consider that for the quadrants (in counter clock-wise order starting from the top right quadrant) you have the following signs for the sines and cosines that follow the relationship:

    sgn(sin(x)) = +, +, -, -
    sgn(cos(x)) = +, -, -, +

    where sgn is the sign (positive or negative) and sin(x), cos(x) are trig functions.

    To understand this you need to consider when the x or y co-ordinate is negative or positive in each quadrant and that the quadrants in terms of angles are divided up into 0,90,180,270 in terms of their relation to quadrants 1,2,3,4.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Super Member
    Joined
    Jul 2012
    From
    INDIA
    Posts
    822
    Thanks
    209

    Re: Trigonometric Functions

    Just remember that when the arm of an angle rotates we get an angle. The rotating arm is always considered positive the sign of the other. Two arms of the triangle is taken depending on the part of axis along which it is measured. For example if the arm of triangle is going upwards form x axis it is taken as positive otherwise negative. Similarly if the other side of the triangle is measured towards right of y axis then it is positive else negative. Going by this logic we see that the sign of both the sides of right angle triangle is positive in first quadrant and negative in fourth quadrant. That is the reason we have tangent positive in first. And fourth quadrant.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Are these trigonometric functions even or odd?
    Posted in the Trigonometry Forum
    Replies: 7
    Last Post: October 6th 2011, 03:35 PM
  2. Replies: 6
    Last Post: August 29th 2010, 05:23 PM
  3. Replies: 3
    Last Post: February 23rd 2010, 04:54 PM
  4. Replies: 2
    Last Post: February 19th 2010, 10:37 AM
  5. Trigonometric functions, arcus functions
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: October 2nd 2009, 04:48 AM

Search Tags


/mathhelpforum @mathhelpforum