If $P\left(x_1, y_1\right)$ is a point such that the length of the tangents from it to the circles…

If $P\left(x_1, y_1\right)$ is a point such that the length of the tangents from it to the circles $x^2+y^2-4 x-6 y-12=0$ and $x^2+y^2+6 x+18 y+26=0$ are in the ratio $2: 3$, then the locus of $P$ is
  1. $x^2+y^2+24 x-36 y+62=0$
  2. $x^2+y^2-24 x+36 y+62=0$
  3. $5x^2+ 5y^2-60x-126y-212=0$
  4. $x^2+y^2+24 x+36 y+62=0$

Solution

Given equations of circle are $ x^2+y^2-4 x-6 y-12=0 $ and $x^2+y^2+6 x+18 y+26=0$ Tangents from $P\left(x_1, y_1\right)$ to the circles are in the ratio of $2: 3$. $ \begin{aligned} & \text { So, } \frac{\sqrt{x_1^2+y_1^2-4 x_1-6 y_1-12}}{\sqrt{x_1^2+y_1^2+6 x_1+18 y_1+26}}=\frac{2}{3} \\ & \Rightarrow \quad \frac{x_1^2+y_1^2-4 x_1-6 y_1-12}{x_1^2+y_1^2+6 x_1+18 y_1+26}=\frac{4}{9} \\ & \Rightarrow 5 x_1^2+5 y_1^2-60 x_1-126 y_1-212=0 \end{aligned} $ Then, the locus of $P\left(x_1, y_1\right)$ is $ 5 x^2+5 y^2-60 x-126 y-212=0 $ No option is correct

Asked in: AP EAMCET 2018 (23 Apr Shift 1)

Practice more Circle questions on Aicharya