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      Question

      Two circles of radii 18 cm and 12 cm touch each other

      externally. Find the length (in cm) of their direct common tangent.
      A 15√6 Correct Answer Incorrect Answer
      B 10√6 Correct Answer Incorrect Answer
      C 12√6 Correct Answer Incorrect Answer
      D 18√6 Correct Answer Incorrect Answer

      Solution

      Given: radius 1 = 18 cm, radius 2 = 12 cm, d = r1 + r2 = 30 cm Length of direct common tangent: {d2 - (r1 - r2)2} = √{302 - (18 - 12)2} = √{900 - 36} = √864 = 12√6 cm

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