Two circles of diameters 4 cm and 16 cm are such that the distance between their centres is 10 cm. What is the length of a common tangent to the circles that does not intersect the line joining the centres?

12 8 10 18

8

Length of direct common tangent = \(\sqrt {d^2-(r_1-r_2)^2}\) = \(\sqrt {10^2-(2-8)^2}\) = \(\sqrt {100-36}\) = 8 cm