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Trig help

  1. Oct 31, 2005 #1
    Ive been given very little notes from my teahcer, and cant do these. looked online, but its was no use.

    1. Using the identities to find the vales of each expression (no calc.)
    (i) sin t = 15/17 , cos t = 8/17 find remaining trig functions
    (ii) sec^2 Pie/12 - tan^2 Pie/12

    2. Find exact value
    (i) tan* = -3 , cos *>0

    3.Use reference angles to find exact value (no calc.)
    (i) cos 225*
    (ii) sin ( -pie/6 )


    Thanks a bunch!
     
  2. jcsd
  3. Oct 31, 2005 #2
    1.(i) Hint : 15^2 + 8^2 = 17^2
    1.(ii) Hint : cos^2(x) = 1 - sin^2(x)
    Divide throughout by [something] to get tan^2(x)

    2.(i) ugly problem
    use my hint for 1.(ii), you may not get exact angle though i am afraid

    3.(i) Hint : 225 = 180 + 45
    3.(ii) Hint : Think what about what i did in 3.(i)

    -- AI
     
  4. Oct 31, 2005 #3

    verty

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    Remember these three identities:

    sin^2 + cos^2 = 1
    sec^2 = 1 + tan^2
    cosec^2 = 1 + cot^2

    Learn them, be able to recite them.

    One more thing, 2.(i) doesn't say 'no calc', so you can use your calculator there. What do the signs mean?
     
    Last edited: Oct 31, 2005
  5. Oct 31, 2005 #4

    mathman

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    For (i), use definitions sec=1/cos, csc=1/sin, tan=sin/cos, cot=cos/sin.
     
  6. Nov 7, 2005 #5
    I'm having trouble proving these trig identities:
    1. sinB+cosBcotB = cscB
    2. (sinA/1-cosA)-cotA = cscA
    3. 2tan13X/1+tan^2 13X = sin26X
    4. secX-tanX/cscX-1 = tanX
     
  7. Nov 8, 2005 #6

    HallsofIvy

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    1. PLEASE don't "hi-jack" someone else's thread for a completely different question- start your own thread.

    2. "Having trouble" implies that you have made an effort. What have you done on these? Have tried converting everything to sine and cosine?

    3. Be careful of your prentheses. A lot of people would interpret "secX-tanX/cscX- 1 as "secX- (tanX/cscX)- 1" but I suspect you mean
    "(secX- tanX)/(cscX-1)".
     
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