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Homework Help: Need help with trigo

  1. Jan 23, 2005 #1
    the question is: find the exact value of tan 285 deg + cos 75 deg + cot 60 deg

    i tried converting them to radians and got

    tan 5pi / 12 + cos 5 pi / 12 + cot pi / 3

    by "exact value", the question means fractions, not decimals. as far as i know, only the cot part has some special identity. am i missing something important? we have a long test tomorrow..

    thanks in advance for any help. ^_^
     
  2. jcsd
  3. Jan 23, 2005 #2

    dextercioby

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    Use the fact that
    [tex] \tan x=\frac{1}{\cot x}=\frac{\sin x}{\cos x} [/tex]

    Daniel.
     
  4. Jan 23, 2005 #3
    that still wouldn't help because 5pi/12 has no special values (i.e. sin pi/6 = 1/2, sin pi/3 = sqrt3 / 2, etc.). it's not a special angle in the unit circle.. :(
     
  5. Jan 23, 2005 #4

    dextercioby

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    [tex] \sin\frac{5\pi}{12}=\sin(\pi-\frac{\pi}{3}-\frac{\pi}{4})=\sin(\frac{2\pi}{3}-\frac{\pi}{4}) [/tex]

    which involves "special angles"...

    Daniel.
     
  6. Jan 23, 2005 #5
    thanks a lot. :)
     
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