Let integers $\mathrm{a}, \mathrm{b} \in[-3,3]$ be such that $\mathrm{a}+\mathrm{b} \neq 0$. Then the number of all possible ordered pairs (a, b), for which $\left|\frac{z-\mathrm{a}}{z+\mathrm{b}}\right|=1$ and $\left|\begin{array}{ccc}z+1 & \omega & \omega^2 \\ \omega & z+\omega^2 & 1 \\ \omega^2 & 1 & z+\omega\end{array}\right|=1, z \in \mathrm{C}$, where $\omega$ and $\omega^2$ are the roots of $x^2+x+1=0$, is equal to _____________ .
Answer (integer)
10
Solution
<p>$$\begin{aligned}
& a, b \in I,-3 \leq a, b \leq 3, a+b \neq 0 \\
& |z-a|=|z+b| \\
& \left|\begin{array}{ccc}
z+1 & \omega & \omega^2 \\
\omega & z+\omega^2 & 1 \\
\omega^2 & 1 & z+\omega
\end{array}\right|=1 \\
& \Rightarrow\left|\begin{array}{ccc}
z & z & z \\
\omega & z+\omega^2 & 1 \\
\omega^2 & 1 & z+\omega
\end{array}\right|=1
\end{aligned}$$</p>
<p>$$\begin{aligned}
& \Rightarrow z\left|\begin{array}{ccc}
1 & 1 & 1 \\
\omega & z+\omega^2 & 1 \\
\omega^2 & 1 & z+\omega
\end{array}\right|=1 \\
& \Rightarrow z\left|\begin{array}{ccc}
1 & 0 & 0 \\
\omega & z+\omega^2-\omega & 1-\omega \\
\omega^2 & 1-\omega^2 & z+\omega-\omega^2
\end{array}\right|=1
\end{aligned}$$</p>
<p>$$\begin{aligned}
&\begin{aligned}
& \Rightarrow z^3=1 \\
& \Rightarrow z=\omega, \omega^2, 1
\end{aligned}\\
&\text { Now }\\
&\begin{aligned}
& |1-\mathrm{a}|=|1+\mathrm{b}| \\
& \Rightarrow 10 \text { pairs }
\end{aligned}
\end{aligned}$$</p>
About this question
Subject: Mathematics · Chapter: Complex Numbers and Quadratic Equations · Topic: Complex Numbers and Argand Plane
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