Sum of squares of modulus of all the complex numbers z satisfying $\overline z = i{z^2} + {z^2} - z$ is equal to ___________.
Answer (integer)
2
Solution
Let $z=x+i y$
<br/><br/>
So $2 x=(1+i)\left(x^{2}-y^{2}+2 x y i\right)$
<br/><br/>
$\Rightarrow 2 x=x^{2}-y^{2}-2 x y\quad$ ...(i) and
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$x^{2}-y^{2}+2 x y=0\quad\dots(ii)$
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From (i) and (ii) we get
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$x=0 \text { or } y=-\frac{1}{2}$
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When $x=0$ we get $y=0$
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When $y=-\frac{1}{2}$ we get $x^{2}-x-\frac{1}{4}=0$
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$\Rightarrow \quad x=\frac{-1 \pm \sqrt{2}}{2}$
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So there will be total 3 possible values of $z$, which are $0,\left(\frac{-1+\sqrt{2}}{2}\right)-\frac{1}{2} i$ and $\left(\frac{-1-\sqrt{2}}{2}\right)-\frac{1}{2} i$
<br/><br/>
Sum of squares of modulus
<br/><br/>
$$
\begin{aligned}
&=0+\left(\frac{\sqrt{2}-1}{2}\right)^{2}+\frac{1}{4}+\left(\frac{\sqrt{2}+1}{2}\right)^{2}=+\frac{1}{4} \\\\
&=2
\end{aligned}
$$
About this question
Subject: Mathematics · Chapter: Complex Numbers and Quadratic Equations · Topic: Complex Numbers and Argand Plane
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