10th Class Mathematics Arithmetic Progressions Question Bank Arithmetic Progressions

  • question_answer
    A circle with area \[{{A}_{1}}\] is contained in the interior of a larger circle with area \[{{A}_{1}}+{{A}_{2}}.\] If the radius of the larger circle is 3 units and \[{{A}_{1}},{{A}_{2}},{{A}_{1}}+{{A}_{2}}\]are in A.P., then the radius of the smaller circle is ___.

    A) \[\sqrt{2}\] units    

    B)        1 unit  

    C) 2 units         

    D) \[\sqrt{3}\] units

    Correct Answer: D

    Solution :

    We have given, \[{{A}_{1}},{{A}_{2}},\,{{A}_{1}}+{{A}_{2}}\] are in A.P. \[\Rightarrow \] \[2{{A}_{2}}={{A}_{1}}+{{A}_{1}}+{{A}_{2}}\,\,\Rightarrow \,\,{{A}_{2}}=2{{A}_{1}}\]   ?.. (i) And \[{{A}_{2}}+{{A}_{1}}=\pi {{(3)}^{2}}\Rightarrow 3{{A}_{1}}=9\pi \]...(using (i) \[\Rightarrow \]   \[{{A}_{1}}=3\pi \,\,\Rightarrow \,\,\pi r_{1}^{2}=3\pi \] [Here y, is the radius of smaller circle.] \[\Rightarrow \]  \[{{r}_{1}}=\sqrt{3}\] units


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