Root of iota?

Algebra Level 3

find i \sqrt{-i} , note i 2 = 1 { i }^{ 2 }=-1 .

± 1 1 ι \pm 1\mp 1\iota 2 ι \mp 2\iota 42 ± 1 2 1 2 ι \pm \frac { 1 }{ \sqrt { 2 } } \mp \frac { 1 }{ \sqrt { 2 } } \iota ι \iota

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2 solutions

Rishabh Jain
Feb 15, 2016

Using i 2 + 1 = 0 \color{#3D99F6}{i^2+1=0} i = 1 2 ( 2 i ) \large \sqrt{-i}=\frac{1}{\sqrt2}(\sqrt{-2i}) = 1 2 ( i 2 + 1 2 i ) \large =\frac{1}{\sqrt2}(\sqrt{\color{#3D99F6}{i^2+1}-2i}) = 1 2 ( i 1 ) 2 \large =\frac{1}{\sqrt2}\sqrt{(i-1)^2} = ± 1 2 1 2 i \Large=\pm \frac { 1 }{ \sqrt { 2 } } \mp \frac { 1 }{ \sqrt { 2 } } i

Gts 07
Feb 15, 2016

l e t t h e r o o t s b e x + y ι i . e ι ( x + y ι ) 2 = ι x 2 y 2 + 2 x y ι = ι c o m p a r i n g r e a l a n d i m a g i n a r y p a r t s , x 2 y 2 = 0 e q ( 1 ) 2 x y = ι e q ( 2 ) u s i n g i d e n t i t y , ( x 2 + y 2 ) 2 = ( x 2 y 2 ) 2 + ( 2 x y ) 2 x 2 + y 2 = 1 e q ( 3 ) ( A s s q u a r e o f r e a l n o . c a n n o t b e n e g a t i v e ) f r o m e q ( 1 ) & e q ( 3 ) x = ± 1 2 s i m i l a r l y , y = ± 1 2 T h e r o o t s a r e ± 1 2 1 2 ι ( b e c a u s e b o t h x a n d y c a n t b e s i m u l t a n e o u s l y p o s i t i v e o r n e g a t i v e a s t h e i r p r o d u c t i s n e g a t i v e e q ( 2 ) . let\quad the\quad roots\quad be\quad x+y\iota \quad i.e\sqrt { -\iota } \\ ({ x+y\iota ) }^{ 2 }=-\iota \\ { x }^{ 2 }-{ y }^{ 2 }+2xy\iota =-\iota \\ comparing\quad real\quad and\quad imaginary\quad parts,\\ { x }^{ 2 }-{ y }^{ 2 }=0\quad eq(1)\\ 2xy=-\iota \quad eq(2)\\ using\quad identity,\\ { { (x }^{ 2 }+{ y }^{ 2 }) }^{ 2 }=({ { x }^{ 2 }-{ y }^{ 2 }) }^{ 2 }+({ 2xy) }^{ 2 }\\ \therefore \quad { x }^{ 2 }+{ y }^{ 2 }=1\quad eq(3)\quad \quad \quad \quad \quad \quad (As\quad square\quad of\quad real\quad no.\quad cannot\quad be\quad negative)\\ from\quad eq(1)\quad \& \quad eq(3)\\ x=\pm \frac { 1 }{ \sqrt { 2 } } \\ similarly,\\ y=\pm \frac { 1 }{ \sqrt { 2 } } \\ \therefore \quad The\quad roots\quad are\quad \pm \frac { 1 }{ \sqrt { 2 } } \mp \frac { 1 }{ \sqrt { 2 } } \iota \\ (because\quad both\quad x\quad and\quad y\quad can't\quad be\quad \quad simultaneously \quad positive\quad or\quad negative\quad as\quad their\quad product\quad is\quad negative\quad eq(2).

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