RRB NTPC Mains or Stage 2 Model Paper 6 with solutions

Question : 13 of 119

Marks: +1, -0

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?

Solution:

r_1 = 9 cm and r_2 = 4

r_1 + r_2 = 9 + 4 = 13

cm
and

r_1 – r_2 = 9 – 4 = 5

cm
Also,

d = 13 cm

Here,

d = r_1 + r_2

= 13 cm Hence, two circles touch each other externally, so there are three common tangents.

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