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Which of the following is equivalent to the complex number 
i^(21) ?
Choose 1 answer:
(A) 1
(B) 
i
(C) -1
(D) 
-i

Which of the following is equivalent to the complex number i21 i^{21} ?\newlineChoose 11 answer:\newline(A) 11\newline(B) i i \newline(C) 1-1\newline(D) i -i

Full solution

Q. Which of the following is equivalent to the complex number i21 i^{21} ?\newlineChoose 11 answer:\newline(A) 11\newline(B) i i \newline(C) 1-1\newline(D) i -i
  1. Determine pattern of powers: Determine the pattern of powers of ii.\newlineThe powers of ii follow a cyclical pattern:\newlinei1=ii^1 = i\newlinei2=1i^2 = -1\newlinei3=ii^3 = -i\newlinei4=1i^4 = 1\newlineThen the pattern repeats every 44 powers.
  2. Reduce exponent modulo 44: Reduce the exponent 2121 modulo 44 to find its equivalent in the pattern.\newline21mod4=121 \mod 4 = 1\newlineThis means that i21i^{21} is equivalent to i1i^{1} in the pattern.
  3. Match reduced exponent to pattern: Match the reduced exponent to the pattern.\newlineSince 21mod4=121 \mod 4 = 1, we look at the pattern and see that i1=ii^1 = i.

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