Two circles touch each other externally. The radius of the first circle with centre A is 18cm. The radius of the second circle with centre B is 8cm.Find the length of their common tangent CD.

24 cm

Length of direct common tangent = √(\( {d }^{2 } \) - \( {(r1\;-\;r2) }^{2 } \))

= √(\( {26 }^{2 } \) - \( {(18\;-\;8) }^{2 } \)) = \(\sqrt {676\;-\;100 }\)

= \(\sqrt { 576}\) = 24 cm

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