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Trig Quadrant Help

  1. Jul 13, 2012 #1
    1. The problem statement, all variables and given/known data

    Determine the following and state quadrant.

    cos(-65°)

    2. Relevant equations

    I make this the 2nd quadrant.


    3. The attempt at a solution

    where:-
    -cos(180 - θ)
    -cos ( 180 - (-65))
    -cos245
    = 0.423

    however i wasnt sure if it lied in the 4th quadrant
    so:-
    -cos(360 - θ)
    -cos ( 360 - (-65))
    -cos425
    = 0.423

    Can anyone help me understand this PPPPUUUUURRRRRRLEASE. :confused:

    Thanks guys.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Jul 13, 2012 #2

    Mentallic

    User Avatar
    Homework Helper

    This will be an easy one to answer if you know how the angles move.

    Basically you start on the positive x-axis and travel in a circle in a counter-clockwise fashion. So at 10o you'll be in the 1st quadrant and very close to the x-axis. At 45o you're half way between the x-axis and y-axis in the 1st quadrant. At 90o you're now on the positive end of the y-axis. You continue to move counter-clockwise and now you've hit the 2nd quadrant.

    Negative angles however are defined as starting at the same point on the x-axis but instead you now move clockwise, so at -10o you're suddenly in the 4th quadrant.
     
  4. Jul 17, 2012 #3
    Sorry for the late response.

    Thank you for the reply all sorted now thanks to ya:)
     
  5. Jul 17, 2012 #4

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    So you have realized that -65° is in the fourth quadrant, not the second?
     
  6. Jul 17, 2012 #5
    Yes i got there in the end. Problem is im doing a self study course and the notes are horrific. Wish i had knuckled down when education was free.

    Thanks:)
     
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