For real numbers $a$ and $b$, if $4 a+i(3 a-b)=b-6 i$ and $z=a+\frac{b}{4} i$, then $\frac{|z|}{a}=$

For real numbers $a$ and $b$, if $4 a+i(3 a-b)=b-6 i$ and $z=a+\frac{b}{4} i$, then $\frac{|z|}{a}=$
  1. $2 \sqrt{2}$
  2. $6 \sqrt{2}$
  3. $\sqrt{2}$
  4. $2$

Solution

$\because 4 a+i(3 a-b)=b-6 i$ Comparing both sides, we get : $\begin{aligned} & 4 a=b \\ & 3 a-b=-6 \Rightarrow 3 a-4 a=-6 \Rightarrow, a=6 \\ & \therefore \quad b=24 \\ & Z=a+\frac{b}{4} i \Rightarrow z=6+\frac{24}{4} i=6+6 i \\ & |z|=\sqrt{36+36}=6 \sqrt{2} \\ & \frac{|z|}{a}=\frac{6 \sqrt{2}}{6}=\sqrt{2} \end{aligned}$

Asked in: AP EAMCET 2023 (17 May Shift 1)

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