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anonymous

  • 5 years ago

Actually, I stand corrected with my question. it is how does cos(-5pi/3)= -square root of 2/2?

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  1. amistre64
    • 5 years ago
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    its proved usually by drawing the angle inside the unit circle

  2. anonymous
    • 5 years ago
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    i saw that unit circle and closed the trig book in fear and ran the other way!!! Do yo have to use the unit circle? If so, how does one read it? Btw, hello again from Illinois. Back for more torture, huh? ; )

  3. amistre64
    • 5 years ago
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    you can use a triangle as well, bu the unit scircle is a better fit; im drawing one u p for you right now

  4. amistre64
    • 5 years ago
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    cos -5pi/3 is just about a full circle so; we can call it pi/3 = 60 cos(60) = 1/2 so i dont see a way to 'prove' it becasue its contradictory it first glance

  5. anonymous
    • 5 years ago
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    yes you have to use the unit circle. put the 'reference triangle' inside it. or just use a cheat sheet. best one is here http://tutorial.math.lamar.edu/cheat_table.aspx

  6. anonymous
    • 5 years ago
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    actually it does not!

  7. amistre64
    • 5 years ago
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  8. amistre64
    • 5 years ago
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    the cos of that angle = 1/2 regardless of any other measures

  9. anonymous
    • 5 years ago
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    \[cos(-\frac{5\pi}{3})+=\frac{1}{2}\]

  10. anonymous
    • 5 years ago
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    so looking at this unit circle. i see on there that 225 degrees, for example, is 5pi/4. but what if i wanted cos or sin? like in my original ? which asks cos(-5pi/4). does it not matter about the cos or sin? will the answer in square root always be the same?

  11. anonymous
    • 5 years ago
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    \[= \]cos(-5pi/3) =cos(5pi/3) =\[cos( 2 \pi - 5\pi/3)\] \[=\cos(\pi / 3)\] = 1/2

  12. amistre64
    • 5 years ago
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    cos is the x value of the angle dropped down to the x axis

  13. amistre64
    • 5 years ago
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    sin is the y value

  14. amistre64
    • 5 years ago
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    like this

  15. amistre64
    • 5 years ago
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  16. anonymous
    • 5 years ago
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    hey are you going to be around today? I am goiong to go investigate this unit circle and maybe I can get somewhere with it then! Thanks again, of course! Too bad you live so far away; i would pay a ton of money for your tutoring math abilities!

  17. amistre64
    • 5 years ago
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    a ton eh ;) i should be around till about 5. cant say much for after that tho

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