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Math Help - Trig Helppppp Please!!!

  1. #1
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    Trig Helppppp Please!!!

    I dont even know where to start on this question!!

    Evaluate: Sin(2Pi/3) and Cos(2Pi/3)
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    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by redpanda11 View Post
    I dont even know where to start on this question!!

    Evaluate: Sin(2Pi/3) and Cos(2Pi/3)
    \sin \frac {2 \pi}3 = \pm \sin \frac {\pi}3 and \cos \frac {2 \pi}3 = \pm \cos \frac {\pi}3. those values you should know. but how do we figure out the signs? we do that by finding out what quadrant the angle \frac {2 \pi}3 is in.

    Remember the mnemonic, All Students Take Calculus

    if it is in the first quad: sine is positive and cosine is positive
    if it is in the second quad: sine is positive and cosine is negative
    if it is in the third quad: sine is negative and cosine is negative
    if it is in the fourth quad: sine is negative and cosine is positive

    so, what's the answer?
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  3. #3
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    sin root 3/2,
    cos -1/2?
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  4. #4
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    sin + pi/3, cos -pi/3
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    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by redpanda11 View Post
    sin root 3/2,
    cos -1/2?
    what? why is there sine and cosine in your answer? the answers are just numbers.

    please type coherently, i'm guessing you mean: \sin \frac {2 \pi}3 = \frac {\sqrt {3}}2 and \cos \frac {2 \pi}3 = - \frac 12

    if so, that's correct

    Quote Originally Posted by redpanda11 View Post
    sin + pi/3, cos -pi/3
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  6. #6
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    sorry i meant root3/2
    and -1/2
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  7. #7
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    sorry!! i understand it to a certain extent but what if it's like tan 19pi/6 how do you know what quadrant it is in??
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  8. #8
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by redpanda11 View Post
    sorry!! i understand it to a certain extent but what if it's like tan 19pi/6 how do you know what quadrant it is in??
    you can keep adding or subtracting 2 \pi if you don't like the size of the angle. you won't change it's value, you just change the number of revolutions to get there. so here, you would realize that \frac {19 \pi}6 \equiv \frac {7 \pi}6
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