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Find all complex numbers z such that z^2 = 2i + 2.

 May 26, 2022
 #1
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0

z = 1 + i/2, 1 - i/2

 May 26, 2022
 #2
avatar+118703 
+1

z^2 = 2i + 2.

 

let Z = a+bi

 

Z^2= a^2-b^2+2abi

 

a2b2=2(1)2ab=2(2)ab=1b=1/aa21a2=2a42a21=0letm=a2m22m1=0...m=1+2orm=12but m is positive som=1+2a=±1+2b=±11+2

 

a=±1+2b=±11+2b=±11+21+21+2b=±1+21+2b=±1+21+2×1212b=±1+212×12121b=±1212×121b=±i1×i211b=±21

You seriously need to check that

 

PLUS I expect it should ahave been done by letting     Z=Aeiθ

 

 

 

LaTex

a^2-b^2=2 \qquad (1)\\2ab=2\qquad (2)\\
ab=1\\
b=1/a\\
a^2-\frac{1}{a^2}=2\\
a^4-2a^2-1=0\\
let\;\;m=a^2\\
m^2-2m-1=0\\
...\\
m=1+\sqrt2\qquad or \qquad m=1-\sqrt2\\
\text{but m is positive so}\\
m=1+\sqrt2\\
a=\pm\sqrt{1+\sqrt2}\\
b=\pm\frac{1}{\sqrt{1+\sqrt2}}

 

a=\pm\sqrt{1+\sqrt2}\\
b=\pm\frac{1}{\sqrt{1+\sqrt2}}\\
b=\pm\frac{1}{\sqrt{1+\sqrt2}}\frac{\sqrt{1+\sqrt2}}{\sqrt{1+\sqrt2}}\\
b=\pm\frac{\sqrt{1+\sqrt2}}{1+\sqrt2}\\
b=\pm\frac{\sqrt{1+\sqrt2}}{1+\sqrt2}\times\frac{1-\sqrt2}{1-\sqrt2}\\
b=\pm\frac{\sqrt{1+\sqrt2}}{1-2}\times\frac{\sqrt{1-\sqrt2}\sqrt{1-\sqrt2}}{1}\\
b=\pm\frac{\sqrt{1-2}}{1-2}\times\frac{\sqrt{1-\sqrt2}}{1}\\
b=\pm\frac{i}{-1}\times \frac{i\sqrt{\sqrt2-1}}{1}\\
b=\pm \sqrt{\sqrt2-1}\\
 

 May 27, 2022
 #3
avatar+33658 
+4

Here's an alternative approach:

 May 28, 2022

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