Answer:
13.86
Step-by-step explanation:
Note m∠ADB = m∠ABC, and m∠A = m∠A, so
ΔABD ~ ΔABC
AD : x = x : AC
AD : x = x : (AD + DC)
12 : x = x : 16
x^2 = 12 * 16 = 192
[tex]x=\sqrt{192} = 13.86[/tex]
