Let $O$ be the origin, the point $A$ be $z_1=\sqrt{3}+2 \sqrt{2} i$, the point $B\left(z_2\right)$ be such…

Let $O$ be the origin, the point $A$ be $z_1=\sqrt{3}+2 \sqrt{2} i$, the point $B\left(z_2\right)$ be such that $\sqrt{3}\left|z_2\right|=\left|z_1\right|$ and $\arg \left(z_2\right)=\arg \left(z_1\right)+\frac{\pi}{6}$. Then
  1. area of triangle ABO is $\frac{11}{\sqrt{3}}$
  2. ABO is an obtuse angled isosceles triangle
  3. area of triangle ABO is $\frac{11}{4}$
  4. ABO is a scalene triangle

Solution


$\begin{aligned}
& O A=\left|z_1\right|=\sqrt{3+8}=\sqrt{11} \\ & \text { and } O B=\frac{1}{\sqrt{3}}\left|z_1\right|=\sqrt{\frac{11}{3}} \\ & A B^2=O A^2+O B^2-2 \cdot O A \cdot O B \cos \frac{\pi}{6} \\ & \quad=11+\frac{11}{3}-2 \cdot \frac{11}{\sqrt{3}} \cdot \frac{\sqrt{3}}{2} \\ & \therefore \quad A B=\sqrt{\frac{11}{3}} \\ & \therefore \quad \text { Area of } \triangle A B D=\frac{1}{2} \cdot O A \cdot O B \cdot \sin \frac{\pi}{6} \\ & \quad=\frac{11}{4 \sqrt{3}} \text { sq. units }
\end{aligned}$
Here $O B=A B$ and $\angle A=\frac{2 \pi}{3}$
$\therefore \quad \triangle A B D$ is an obtuse angled isosceles triangle.

Asked in: JEE Main 2025 (28 Jan Shift 1)

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