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# FP2 Further Complex Numbers

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1. Hi, got TWO questions in my FP2 book, but couldnt find the way to solve it.

For the first one,i cant prove it. i have no idea what kind of mistakes that i made. The following is my working

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
2. 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
3. Where you wrote (2 lines from the bottom) - instead write then work from there.
4. (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
5. (Original post by dantheman1261)
Where you wrote (2 lines from the bottom) - instead write then work from there.
thanks

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