Answer:
9 cm
Step-by-step explanation:
In a 30°-60°-90° triangle, the ratio of the shortest to the longest sides is 1 : 2.
That means DB = 1/2BC = 3 cm. It also means AB = 2BC = 12 cm.
Then the length of AD is ...
AD +DB = AB
AD = AB -DB = 12 cm -3 cm
AD = 9 cm
