JEE Main & Advanced Mathematics Circle and System of Circles Question Bank System of circles

  • question_answer
    A circle with radius 12 lies in the first quadrant and touches both the axes, another circle has its centre at (8,9) and radius 7. Which of the following statements is true

    A)            Circles touch each other internally

    B)            Circles touch each other externally

    C)            Circles intersect at two distinct points

    D)            None of these

    Correct Answer: A

    Solution :

               \[{{r}_{1}}=\sqrt{{{g}^{2}}+{{f}^{2}}-c}=12\]                    Also \[r=-g=-f=12\] (because it touches both the axes)                    \[\Rightarrow {{C}_{1}}=(12,\ 12),\ {{r}_{2}}=7,\ {{C}_{2}}=(8,\ 9)\]                    Now \[{{C}_{1}}{{C}_{2}}=5\] and \[{{r}_{1}}-{{r}_{2}}=5\]                    Therefore, circles touch each other internally.


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