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Homework Help: Equivalent Expressions

  1. Oct 27, 2016 #1
    1. The problem statement, all variables and given/known data
    State an equivalent expression in terms of the related acute angle?
    (A) cot(-π/4)

    2. Relevant equations

    3. The attempt at a solution
    (A) I made the the unit circle and since its negative I went clockwise and made it into the fourth quadrant. I ended up getting -cotπ/4. However the answer is not the one that the text book has given. Im a little confused.
    The text book has given the answer cot3π/4, but I thought we were supposed to go clockwise because it is negative?
  2. jcsd
  3. Oct 27, 2016 #2


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    Science Advisor
    Homework Helper
    Gold Member

    An acute angle is one that is less than ##\pi /2##. I've never seen this used for negative angles, so I'm not sure whether ##-\pi /4## would be considered acute. In any case, ##3\pi /4## is not an acute angle. It's actually a "reflex" angle (I had to look that one up).

    I thought your answer was correct. ##\pi /4## is definitely an acute angle.
    Last edited: Oct 27, 2016
  4. Oct 27, 2016 #3


    Staff: Mentor

    I agree with @PeroK -- ##3\pi/4## is not an acute angle.
    I'll bet what you actually looked up was "reflex". :oldbiggrin:
  5. Oct 27, 2016 #4
    I just asked my teacher, I got the angle correct. Thx.
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