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9th Class Mathematics Circles Question Bank Circle

  • question_answer
    In the given figure below, two circles with their centres at O and P and radii 9 cm and 4 cm respectively touch each other externally. The length of their common tangent is

    A)  8.5 cm.                       

    B)  \[\frac{8}{\sqrt{2}}\] cm.

    C)  \[8\sqrt{2}\]cm.                        

    D)  12cm.

    Correct Answer: D

    Solution :

    (d): Common tangent  \[=\sqrt{{{\left( 9+4 \right)}^{2}}-{{\left( 9-4 \right)}^{2}}}\] \[=\sqrt{{{13}^{2}}-{{5}^{2}}}\] \[=\sqrt{144}\] = 12 cm


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