Answer:
AD = 9 cm
Step-by-step explanation:
Recognize all of the triangles are 30°-60°-90° triangles that have side ratios of 1 : √3 : 2. That is, the longest side is double the length of the shortest side.
CB = 2(DB)
DB = CB/2 = (6 cm)/2 = 3 cm
AB = 2(CB)
AB = 2(6 cm) = 12 cm
AD +DB = AB
AD +3 cm = 12 cm
AD = 9 cm . . . . . . . . . . subtract 3 cm
