The diameter of two circles are 18 cm and 8 cm. The distance between their centres is 13 cm. What is the number of common tangents?



[ A ]    1
[ B ]    2
[ C ]    3 right
[ D ]    None of These
Answer : Option C
Explanation :
Here, r1 = 9 cm and r 2 = 4 cm
r 1 + r 2 = 9 + 4 = 13 cm
and r 1 – r 2 = 9 – 4 = 5cm
Also, d = 13 cm
Here, d = r 1 + r 2
= 13 cm
Hence, two circles touch each other externally, so three total no of common tangents are three.

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