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Question: Answered & Verified by Expert
The locus of the center of a variable circle which always touches two given circles externally is
MathematicsHyperbolaWBJEEWBJEE 2021
Options:
  • A an ellipse
  • B a hyperbola
  • C a parabola
  • D a circle
Solution:
2061 Upvotes Verified Answer
The correct answer is: a hyperbola


$\begin{array}{l}
\mathrm{oo}_{1}=\mathrm{r}+\mathrm{r}_{1} \\
\mathrm{oo}_{2}=\mathrm{r}+\mathrm{r}_{2} \\
\therefore \mathrm{oo}_{2}-\mathrm{oo}_{1}=\mathrm{r}_{2}-\mathrm{r}_{1}
\end{array}$
hence, locus is hyperbola

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