Wednesday, November 16, 2011

Find the imaginary part of the complex number(1+i)^10 + (1-i)^10.

We'll recall the rectangular form of a complex
number:


z = a + b*i, where a is the real part and b is the
imaginary part.


We notice that we can write (1+i)^10 =
[(1+i)^2]^5


We'll expand the
binomial:


(1+i)^2 = 1 + 2i +
i^2


We'll replace i^2 by
-1:


(1+i)^2 = 1 + 2i - 1


We'll
eliminate like terms:


(1+i)^2 =
2i


(1+i)^10 = (2i)^5 =
2^5*i^5


We know that i^5 = i^4*i = 1*i =
i


(1+i)^10 = 32 i (1)


We
notice that we can write (1-i)^10 = [(1-i)^2]^5


We'll
expand the binomial:


(1-i)^2 = 1 - 2i +
i^2


(1-i)^2 = -2i


(1-i)^10 =
(-2i)^5 = -32i (2)


We'll add (1) +
(2):


(1-i)^2 + (1-i)^10 = 32 i - 32
i


(1-i)^2 + (1-i)^10 = 0


We
can write the result as a complex number, as it
follows:


(1-i)^2 + (1-i)^10 = 0 +
0i


We notice that the imaginary part of the
complex number is b = 0.

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