Imaginary number challenge(2)

Algebra Level 5

( 1 + i 2 i ) 3 + i = a e π / b \large \left|\left(\sqrt[2-i]{1+i}\right)^{3+i}\right| = \sqrt a e^{-\pi/b}

The expression above holds true for positive integers a a and b b , where a a is square free.

Find the value of 63 a 3 b 63a^{3}b .

Notations :

Hint : Euler's Formula is the core of this problem.


The answer is 2016.

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1 solution

Tommy Li
Jun 21, 2016

( 1 + i 2 i ) 3 + i \large |(\sqrt[2-i]{1+i})^{3+i}|

= ( 1 + i ) 3 + i 2 i =\large |(1+i)^{\frac{3+i}{2-i}}|

= ( 1 + i ) 3 + i 2 i × 2 + i 2 + i =\large |(1+i)^{\frac{3+i}{2-i} \times \frac{2+i}{2+i}}|

= ( 1 + i ) 5 + 5 i 5 =\large |(1+i)^{\frac{5+5i}{5}}|

= ( 1 + i ) 1 + i =\large |(1+i)^{1+i}|

= ( 2 e π 4 i ) 1 + i =\large |(\sqrt{2}e^{\frac{\pi}{4}i})^{1+i}|

= ( 2 e π 4 i ) ( ( 2 ) i e π 4 ) =\large |(\sqrt{2}e^{\frac{\pi}{4}i})((\sqrt{2})^{i}e^{-\frac{\pi}{4}})|

= ( 2 e π 4 ) ( ( 2 ) i e π 4 i ) =\large |(\sqrt{2}e^{-\frac{\pi}{4}})((\sqrt{2})^{i}e^{\frac{\pi}{4}i})|

= ( 2 e π 4 ) ( e ( ln 2 + π 4 ) i ) =\large |(\sqrt{2}e^{-\frac{\pi}{4}})(e^{(\ln{\sqrt{2}}+\frac{\pi}{4})i})|

= ( 2 e π 4 ) ( e ( ln 2 + π 4 ) i ) =\large (\sqrt{2}e^{-\frac{\pi}{4}})|(e^{(\ln{\sqrt{2}}+\frac{\pi}{4})i})|

= ( 2 e π 4 ) ( 1 ) =\large (\sqrt{2}e^{-\frac{\pi}{4}})(1)

= ( 2 e π 4 ) =\large (\sqrt{2}e^{-\frac{\pi}{4}})

63 a 3 b = 63 ( 2 ) 3 ( 4 ) = 2016 \Rightarrow 63a^{3}b= 63(2)^{3}(4) = 2016


e π 4 = cos ( π 4 ) + i sin ( π 4 ) e^{\frac{\pi}{4}} = \cos(\frac{\pi}{4})+i\sin(\frac{\pi}{4})

e π 4 = 2 2 + i 2 2 e^{\frac{\pi}{4}} = \frac{\sqrt{2}}{2}+i\frac{\sqrt{2}}{2}

( 2 ) e π 4 = ( 2 ) 2 2 + ( 2 ) i 2 2 (\sqrt{2})e^{\frac{\pi}{4}} = (\sqrt{2})\frac{\sqrt{2}}{2}+(\sqrt{2})i\frac{\sqrt{2}}{2}

2 e π 4 = 1 + i \sqrt{2}e^{\frac{\pi}{4}} = 1+i


e i x = cos ( x ) 2 + sin ( x ) 2 |e^{ix}| = \sqrt{\cos(x)^{2} + \sin(x)^{2}}

e i x = 1 |e^{ix}| =1

( e ( ln 2 + π 4 ) i ) = 1 \Rightarrow |(e^{(\ln{\sqrt{2}}+\frac{\pi}{4})i})| = 1

e π 4 e π 4 i e^{\dfrac{\pi}{4}} \neq e^{\dfrac{\pi}{4}i} although e π 4 i = cos π 4 + i sin π 4 . e^{\dfrac{\pi}{4}i} = \cos{\dfrac{\pi}{4}} + i\sin{\dfrac{\pi}{4}}. e π 4 e^{\dfrac{\pi}{4}} is simply e π 4 . e^{\dfrac{\pi}{4}}. Excuse my LaTeX

Akeel Howell - 4 years, 5 months ago

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