Q49 / 75 · JEE Main 2025 (7 Apr Shift 1) · Mathematics
If for $\theta \in\left[-\frac{\pi}{3}, 0\right]$, the points $(x, y)=\left(3 \tan \left(\theta+\frac{\pi}{3}\right), 2 \tan \left(\theta+\frac{\pi}{6}\right)\right)$ lie on $x y+\alpha x+\beta y+\gamma=0$, then $\alpha^2+\beta^2+\gamma^2$ is equal to :
- A80
- B72
- C96
- Correct answerD75
Solution
$\begin{aligned}<br/>& x=3\left(\frac{\tan \theta+\sqrt{3}}{1-\sqrt{3} \tan \theta}\right) \\
& x-\sqrt{3} \tan \theta=3 \tan \theta+3 \sqrt{3} \\
& \tan \theta=\frac{x-3 \sqrt{3}}{3+\sqrt{3} x} \ldots(1) \\
& 2\left(\frac{\tan \theta+\frac{1}{\sqrt{3}}}{1-\frac{\tan \theta}{\sqrt{3}}}=y\right) \\
& 2(\sqrt{3} \tan \theta+1)=y(\sqrt{3}-\tan \theta) \ldots .<br/>\end{aligned}$
using (1) and (2)
$\begin{aligned}<br/>& 2\left(\frac{x-3 \sqrt{3}}{\sqrt{3}+x}+1\right)=y\left(\sqrt{3}-\frac{(x-3 \sqrt{3})}{\sqrt{3}(\sqrt{3}+x)}\right) \\ & 2 \sqrt{3}(x-3 \sqrt{3}+x+\sqrt{3})=y(3(\sqrt{3}+x)-x+3 \sqrt{3}) \\ & 4 \sqrt{3} x-12=y(2 x+6 \sqrt{3}) \\ & x y-2 \sqrt{3} x+3 \sqrt{3} y-6=0 \\ & \Rightarrow \alpha=-2 \sqrt{3}, \beta=3 \sqrt{3}, \gamma=-6 \\ & \alpha^2+\beta^2+\gamma^2=12+27+36=75<br/>\end{aligned}$
using (1) and (2)
$\begin{aligned}<br/>& 2\left(\frac{x-3 \sqrt{3}}{\sqrt{3}+x}+1\right)=y\left(\sqrt{3}-\frac{(x-3 \sqrt{3})}{\sqrt{3}(\sqrt{3}+x)}\right) \\ & 2 \sqrt{3}(x-3 \sqrt{3}+x+\sqrt{3})=y(3(\sqrt{3}+x)-x+3 \sqrt{3}) \\ & 4 \sqrt{3} x-12=y(2 x+6 \sqrt{3}) \\ & x y-2 \sqrt{3} x+3 \sqrt{3} y-6=0 \\ & \Rightarrow \alpha=-2 \sqrt{3}, \beta=3 \sqrt{3}, \gamma=-6 \\ & \alpha^2+\beta^2+\gamma^2=12+27+36=75<br/>\end{aligned}$
Hence, the correct answer is option: 'D'.