math (trig)

posted by .

how do you solve for x?

2cos^24x-1=0

  • math (trig) -

    First find the cos of 24
    multiply this by 2
    add 1 to the other side
    Finally, divide that answer with 1
    and... u have the answer!!! whatever that is...

  • math (trig) -

    I am reading your question as
    2cos^2 (4x) - 1 = 0
    so cos^2 (4x) = 1/2
    cos 4x = ±1/√2

    so 4x must be an angle in each of the 4 quadrants.
    but I know cos 45º = 1/√2
    so 4x = 45 or 4x = 135 or 4x = 225 or 4x = 315
    then
    x = 11.25 or x = 33.75 or x=56.25 or x=78.75

    the period of cos 4x = 90º
    so by adding/subtracting multiples of 90 to any of the above answers will produce other answers
    e.g. 33.75 + 90 = 123.75 would be another possible answer

    proof:
    LS
    = 2 cos^2 (4*123.75) - 1
    = 2cos^2 (495) - 1
    = 2(1/2) - 1
    = 0 = RS

  • math (trig) -

    just follow my way, its much simpler

  • math (trig) -

    MC, except you don't get the right answer, lol

  • math (trig) -

    prove it Reiny
    :)
    my way always works

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