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FP2 Further Complex Numbers

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    Hi, got TWO questions in my FP2 book, but couldnt find the way to solve it.
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    For the first one,i cant prove it. i have no idea what kind of mistakes that i made. The following is my working
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    For the second one, i can do part a and b by myself, but i dun know how to do part c by using the answer in part b.
    Thanks
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    for second question write tan theta =x in rhs. now ignoring lhs what does rhs need to equal to match the x^4... equation?
    for first question you need to use

    (2cosx)^6=(z+1/z)^6

    which follows from the following with n=1

    z^n=cosnx+isin nx

    z^(-n)=cosnx-isin nx

    giving z^(n)+z^(-n)=2cos nx

    and the above will help when you exapnd (z+1/z)^n
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    Where you wrote (2 lines from the bottom)  cos^{4}(\theta) = (\frac{1}{2}cos(4 \theta) + \frac{1}{2}) - instead write  cos^{4}(\theta) = (cos^{2}(\theta))^{2} then work from there.
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    (Original post by mathz)
    for second question write tan theta =x in rhs. now ignoring lhs what does rhs need to equal to match the x^4... equation?
    i still cant get your meaning
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    (Original post by dantheman1261)
    Where you wrote (2 lines from the bottom)  cos^{4}(\theta) = (\frac{1}{2}cos(4 \theta) + \frac{1}{2}) - instead write  cos^{4}(\theta) = (cos^{2}(\theta))^{2} then work from there.
    thanks
 
 
 
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