If two circles of radii 18 cm and 8 cm touch externally, then the length of a direct common tangent is :

24 cm

Formula to be used

2\(\sqrt {R1\; × \; R2 }\)

Calculations

R1 = 18 cm.

R2 = 8 cm.

So, direct common tangent = 2\(\sqrt {18\; × \; 8 }\)

⇒ 2\(\sqrt {144}\)

⇒ 2 x 12

⇒ 24 cm

Therefore, the length of direct common tangent is 24 cm.