Q108 / 160 · WBJEE 2012 · Mathematics
The incentre of an equilateral triangle is (1,1) and the equation of ene side is $3 x+4 y+3=0 .$ Then, the equation of the circumeircle of the triangle is
- A$x^{2}+y^{2}-2 x-2 y-2=0$
- Correct answerB$x^{2}+y^{2}-2 x-2 y-14=0$
- C$x^{2}+y^{2}-2 x-2 y+2=0$
- D$x^{2}+y^{2}-2 x-2 y+14=0$
Solution
since, triangle is equilateral the refore incentre
(1,1) lies on the centroid of the $\Delta A B C$. $\therefore G D=$ Length of perpendicular from the point $G(1,1)$ to the line $3 x+4 y+3=0$
$A G=2 G D=4$
$\therefore$ Equation of circumcircle with centre at (1,1)
$$
\begin{array}{l}
\text { and radius = } \begin{aligned}
4 \text { units } \\
(x-1)^{2}+(y-1)^{2} &=4^{2} \\
\Rightarrow \quad x^{2}+y^{2}-2 x-2 y-14 &=0
\end{aligned}
\end{array}
$$
$A G=2 G D=4$
$\therefore$ Equation of circumcircle with centre at (1,1)
$$
\begin{array}{l}
\text { and radius = } \begin{aligned}
4 \text { units } \\
(x-1)^{2}+(y-1)^{2} &=4^{2} \\
\Rightarrow \quad x^{2}+y^{2}-2 x-2 y-14 &=0
\end{aligned}
\end{array}
$$Hence, the correct answer is option: 'B'.