Root Of Complex?

Algebra Level 5

i 1 / 16 \LARGE i^{{1} / {16}}

Which of the following could be the conjugate of the above complex number?

Notation : cis ( x ) = cos ( x ) + i sin ( x ) \text{cis}(x) = \cos(x) + i \sin(x) .

cis π 8 \text{cis} \frac{\pi}{8} cis π 128 \text{cis} \frac{\pi}{128} None of these choices cis π 16 \text{cis} \frac{\pi}{16} cis π 64 \text{cis} \frac{\pi}{64} cis π 4 \text{cis} \frac{\pi}{4} cis π 2 \text{cis} \frac{\pi}{2} cis π 32 \text{cis} \frac{\pi}{32}

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2 solutions

Gamal Sultan
Apr 13, 2015

The principal amplitude (or proper amplitude) of i is (Pi/2)

So

i = cis (Pi/2)

Then

i^(1/16) = cis (Pi/32 + k Pi/8) , k = 0 , 1 , 2 , 3 , ......... , 15

The conjugate of cic (x) = cis (2 Pi - x)

Then

The conjugate of i^(1/16) = cis (2 Pi - Pi/32 - k Pi/8) , k = 0 , 1 , 2 , 3 , ......... , 15

= cis (Pi/32)(63 - 4 k) , k = 0 , 1 , 2 , 3 , ......... , 15

This does not equal any of the given values for any of the 16 values of k

Saurav Pal
Apr 9, 2015

ι 1 16 = c i s π 32 \iota^\frac{1}{16}=cis \frac{\pi}{32} \Rightarrow Conjugate Of i 1 16 i^\frac{1}{16} = c i s π 32 cis \frac{-\pi}{32} . So the answer is N o n e O f T h e O p t i o n s \boxed{None Of The Options} .

Note that i 1 16 i ^ \frac{1}{16} is a multivalued function, so you should also check the other values.

Calvin Lin Staff - 6 years, 2 months ago

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Conjugate of ι 1 16 = c i s ( k π 16 π 32 ) \iota^{\frac{1}{16}}=cis \ (-\frac{k\pi}{16}-\frac{\pi}{32}) .

Note : k k = 0, 1, 2, . . . . . . , 15.

Saurav Pal - 6 years, 2 months ago

Oh!! Gosh!! I forgot the conjugate!!, perhaps it's because that it's a level 5 prob.

Kunal Gupta - 6 years, 2 months ago

Conjugate-conjure me.Argh!missed the conjugate.

Gautam Sharma - 6 years, 2 months ago

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This should have been a troll question.

Gautam Sharma - 6 years, 2 months ago

Same mistake. I forgot to calculate the conjugate. :(

Yash Choudhary - 6 years, 2 months ago

Missed the conjugate term, ended up marking at wrong option

Prakash Chandra Rai - 6 years, 2 months ago

Hm... Time to research the definition of conjugate!

Julian Poon - 6 years, 2 months ago

forgot to take conjugate !!!...ufff

Aayushi Jain - 6 months, 4 weeks ago

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