AB and CD are two common tangents to circles which touch each other at C. If D lies on AB such that CD = 4 cm, then find the length of AB.
8 cm
Given that CD = 4 cm
We know that CD = DB (tangents from an external point to a circle are equal)
Therefore DB = 4 cm
Also AD = DC (tangents from an external point to a circle are equal)
Therefore AD = 4 cm
Now AB = AD + DB = 4 + 4 = 8 cm
Therefore, the length of AB is 8 cm.