If the set $\left\{\operatorname{Re}\left(\frac{z-\bar{z}+z \bar{z}}{2-3 z+5 \bar{z}}\right): z \in \mathbb{C}, \operatorname{Re}(z)=3\right\}$ is equal to
the interval $(\alpha, \beta]$, then $24(\beta-\alpha)$ is equal to :
Solution
Let $z_1=\left(\frac{z-\bar{z}+z \bar{z}}{2-3 z+5 \bar{z}}\right)$<br/><br/>
Let $\mathrm{z}=3+\mathrm{iy}$<br/><br/> $\bar{z}=3-i y$<br/><br/>
$$
\begin{aligned}
& z_1=\frac{2 i y+\left(9+y^2\right)}{2-3(3+i y)+5(3-i y)} \\\\
& =\frac{9+y^2+i(2 y)}{8-8 i y} \\\\
& =\frac{\left(9+y^2\right)+i(2 y)}{8(1-i y)} \\\\
& \operatorname{Re}\left(z_1\right)=\frac{\left(9+y^2\right)-2 y^2}{8\left(1+y^2\right)}
\end{aligned}
$$<br/><br/>
$$
\begin{aligned}
& =\frac{9-y^2}{8\left(1+y^2\right)} \\\\
& =\frac{1}{8}\left[\frac{10-\left(1+y^2\right)}{\left(1+y^2\right)}\right] \\\\
& =\frac{1}{8}\left[\frac{10}{1+y^2}-1\right] \\\\
& 1+y^2 \in[1, \infty] \\\\
& \frac{1}{1+y^2} \in(0,1] \\\\
& \frac{10}{1+y^2} \in(0,10] \\\\
& \frac{10}{1+y^2}-1 \in(-1,9] \\\\
& \operatorname{Re}\left(\mathrm{z}_1\right) \in\left(\frac{-1}{8}, \frac{9}{8}\right] \\\\
& \alpha=\frac{-1}{8}, \beta=\frac{9}{8} \\\\
& 24(\beta-\alpha)=24\left(\frac{9}{8}+\frac{1}{8}\right)=30
\end{aligned}
$$
About this question
Subject: Mathematics · Chapter: Complex Numbers and Quadratic Equations · Topic: Complex Numbers and Argand Plane
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