Engineering Board Exam Reviewer · Circles · hard

Two circles of radii 9 and 4 have centers 15 units apart. Find the length of their common external tangent.

  1. 7.48
  2. 15
  3. 14.14
  4. 10

Answer

C. 14.14

Solution

For an external tangent, t=sqrt(d2-(r1-r2)2)=sqrt(152-52)=sqrt(200)=14.14.

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