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Math Help - Solving a trig equation?

  1. #1
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    Solving a trig equation?

    I need to solve the following trig expression:

    4cos4θ=0 (reads four cosine four theta)

    Its the formula of a graph but i need to find the zeros or the points that it passes through the pole (its a polar graph)

    Would i use the double angle formula or find when cos=0 and multiply the period by 4? Im confused
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  2. #2
    Junior Member
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    I think you are making this more difficult than it really is....

    4cos4θ=0

    the four is insignificant (because 0/4 is still 0). so now we have:

    cos4θ=0.

    I think the 4 is confusing you so let x=4θ so now we have:

    cosx=0
    and the solutions to that is when x=pi/2 or 3pi/2

    now substitute 4θ in for x and you have
    4θ=pi/2 and 4θ=3pi/2
    so dividing by four yields:
    θ=pi/8 and θ=3pi/8

    Hope that helped!!
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  3. #3
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    Also what domain are you looking for solutions in?

    The previous post gives the solutions on x \in \left[0,\frac{\pi}{2}\right]

    You can find all solutions as x = \frac{(2n+1)\pi}{8}, n\in \mathbb{Z}
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