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Express the complex number $i^{-39}$ in the form $a+ib$

$(a)\;2i\qquad(b)\;i\qquad(c)\;0\qquad(d)\;-i$

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1 Answer

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Answer : $\;i$
Explanation :
$i^{-39} = i^{-4 \times 9-3}$
$= (i^{4})^{-9} \;. i^{-3}$
$ = (1)^{-9} \; . i^{-3} \qquad [i^{4} =1]$
$ = \large\frac{1}{i^{3}} = \large\frac{1}{-i} \qquad [i^{3} =-i]$
$ = -\large\frac{1}{i} \times \large\frac{i}{i}$
$= \large\frac{-i}{i^2}$
$= \large\frac{-i}{-1} \qquad [i^{2} =-1]$
$ = i$
answered Apr 9, 2014 by yamini.v
 

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