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Determine Value of Trig Functions

  1. Jan 10, 2005 #1
    My question is to determine the values of the primary and secondary tri functions at (-3,-4) on the terminal arm of an angle theta in standard position

    Im just wondering how do u know which quadrant this point is in? I have assumed it is in quadrant 1. Then that means x=-3, y=-4, and r=5?

    When determining values for trig functions for example lets say
    [tex] \sin= \frac {opposite} {hypotenuse} = \frac {-4} {5} [/tex] is this the value they want me to determine or do I have to put it in decimals?
     
  2. jcsd
  3. Jan 11, 2005 #2

    dextercioby

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    IIRC,the point of coordinates x=-3,y=-4 is in the 3-rd quadrant.Its distance to the center is 5.

    Can u take it from here??

    Daniel.
     
  4. Jan 11, 2005 #3
    yes just tell me how u know its in the third quadrant? and all I have to do is put opposite/hyp and then adj/hyp etc to determine the values for all the tri functions right?
     
  5. Jan 11, 2005 #4
    This image should help you.

    [​IMG]
     
  6. Jan 11, 2005 #5

    dextercioby

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    BECAUSE THE COORDINATES OF THE POINT ARE BOTH NEGATIVE:If "x" is negative,then it's either in the II-nd or the III-rd quadrant.If "y" is negative it's either in the III-rd or the IV-th quadrant.

    Figure out what happens if both are negative at the same time...

    For the second part,"YES".

    Daniel.
     
  7. Jan 11, 2005 #6

    BobG

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    I would memorize that drawing Recon linked to. If you look at it as a graph (which it is), it's pretty self-explanatory why cosines are positive in Q1 and Q4 and why sines are positive in Q1 and Q2. But, knowing that drawing one way or the other is pretty much essential for most of the trig problems you're doing.
     
  8. Jan 12, 2005 #7
    yes recon's diagram is good I was thinking something more complicated lol i know that going to the left will become negative in the x axis and down is negative in the y axis thanks for explainging and making it more clear.
     
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