Let $\alpha$ and $\beta$ be the sum and the product of all the non-zero solutions of the equation $(\bar{z})^2+|z|=0, z \in C$. Then $4(\alpha^2+\beta^2)$ is equal to :
Solution
<p>$$\begin{aligned}
& (\bar{z})^2+|z|=0 \quad \text{... (1)}\\
& z^2+|\bar{z}|=0 \quad \text{... (2)}
\end{aligned}$$</p>
<p>From equation (1) and (2)</p>
<p>$$\begin{aligned}
& \text { as }|z|=|\bar{z}| \\
& \Rightarrow \quad(\bar{z})^2=z^2 \\
& \Rightarrow \quad z=\bar{z} \text { or } z=-\bar{z} \\
& \Rightarrow \operatorname{Im}(z)=0 \text { or } \operatorname{Re}(z)=0
\end{aligned}$$</p>
<p>Case I : If $\operatorname{Im}(z)=0$</p>
<p>$\Rightarrow z=x$</p>
<p>Putting value of $z$ in equation (1)</p>
<p>$$\begin{aligned}
& x^2+|x|=0 \\
& \Rightarrow x=0 \quad \text{[Rejected]
}
\end{aligned}$$</p>
<p>Case II : If $\operatorname{Re}(z)=0$</p>
<p>$\Rightarrow z=i y$</p>
<p>Putting value of $z$ in equation (1)</p>
<p>$$\begin{aligned}
& -y^2+|y|=0 \\
& y= \pm 1 \text { as } y \neq 0
\end{aligned}$$</p>
<p>Hence, $z= \pm i$ are the solution of the given equation</p>
<p>$$\begin{aligned}
& \Rightarrow \alpha=i-i=0 \\
& \text { and } \beta=i(-i)=1 \\
& \Rightarrow \quad 4\left(\alpha^2+\beta^2\right)=4(0+1) \\
& \quad=4
\end{aligned}$$</p>
<p>$\therefore$ Option (3) is correct</p>
About this question
Subject: Mathematics · Chapter: Complex Numbers and Quadratic Equations · Topic: Complex Numbers and Argand Plane
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