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Homework Help: Trig function help

  1. Jan 25, 2015 #1
    Last edited: Jan 25, 2015
  2. jcsd
  3. Jan 25, 2015 #2
    Can you give the entire problem?
  4. Jan 25, 2015 #3
    all thats given is that
  5. Jan 25, 2015 #4
    What is the question? What are you asked to find?
  6. Jan 25, 2015 #5
    what is =cos2x
  7. Jan 25, 2015 #6
    What is x supposed to be? Is the given problem in terms of t? Are you trying to solve for t and then plug that value in for x?
  8. Jan 25, 2015 #7
    oh my bad its cos2t

    its basically asking you to use the double angle formula
    but im not sure how to find those values
  9. Jan 25, 2015 #8
    If you're simply trying to find t, then use cot = 1/tan... If you have a value for t why do you need to use the double angle identities?
  10. Jan 25, 2015 #9
    to find what cos2t is ....

    you can find what tan is from cot
    then i drew a triangle and got the hypot to be sqrt(41)

    but how do i do that math

    formula for cos2t = cos^2(t) - sin^2(t)
  11. Jan 25, 2015 #10
    Are you forbidden from using a calculator?
  12. Jan 25, 2015 #11
    teacher said u can use it
    but need to know how to do it without one for test
  13. Jan 25, 2015 #12
    Well that may have been useful information at the start...

    you have cot = -5/4, find what tan is then recall tan = sin/cos ... or recall cot = cos/sin...
  14. Jan 25, 2015 #13
    well i worked it out and i believe i got the answer to be 9/41
  15. Jan 25, 2015 #14
    That's what I'm getting
  16. Jan 25, 2015 #15
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