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Homework Help: Trigonometry question

  1. Feb 27, 2012 #1

    I'm studying for an exam and am stuck on a trigonometry question. Could anybody help me out?

    The question is:

    Solve the equation cos3x = 1/2, for x is an element of R, (where x is in radians)

    The answer is:

    x = pi/9 + 2npi/3


    x = 5pi/9 + 2npi/3

    where n is an element of Z

    Sincere thanks


    My attempt

    Well we know that cos (pi/3) = 1/2

    But cos 3x = 1/2 and are trying to figure out what x is.

    So what times 3 will give you pi/3. That would be pi/6.

    3 * (pi/6) = pi/3

    cos (3*(pi/6)) = 1/2
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Feb 27, 2012 #2
    'Well we know that cos (pi/3) = 1/2'
    cos 3x = 1/2
  4. Feb 27, 2012 #3

    It says that the answer is

    x = pi/9 + 2npi/3


    x = 5pi/9 + 2npi/3
  5. Feb 27, 2012 #4
    That is correct, when is Cos(a)=Cos(b)?
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