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

24 cm 14 cm  16 cm  12 cm

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.