In ΔABC is the bisector of ∠A meeting BC at D. If AC = 21 cm, BC = 11 cm and the length of BD is 3 cm less than DC, then the length(in cm) of side AB is:

10 15 18 12

12

Let the length of CD be x = x + 3 - 3 = 11 = 2x - 3 = 11 = 2x = 14 = x = 7 Length of BD = 7 - 3 = 4 From angle bisector property \(\frac{AB}{4}\) = \(\frac{21}{7}\) = AB = 4 x 3 = 12 cm. Therefore, length of AB is 12 cm.