2017 · Q66
The distance between the centres of two circles having radii 9 cm and 4 cm is 13 cm. What is the length of the direct common tangent of these circles ?
Elementary MathematicsCircles
- A12 cm
- B11 cm
- C10 cm
- D9.5 cm
Explanation
Direct common tangent = √(d²−(r₁−r₂)²) = √(169−25) = √144 = 12 cm. Hence option (A) 12 cm. (Trap: using (r₁+r₂) gives the transverse common tangent, 0 here.)