Answer:
C. 8 is the correct answer.
Step-by-step explanation:
Let <DAB be x°
Now,
taking x as reference angle in triangle ADB,
cosx = b/h
or, cosx = 4/AB
Now,
again taking x as reference angle in triangle ACB,
cosx = b/h
or, cosx = AB/20
Now,
cosx = AB/20 = 4/AB
or, AB/20 = 4/AB
or, AB² = 80
Now,
Using pythagoras theorem in triangle ABD,
h² = p² + b²
or, AB² = BD² + AD²
or, 80 = BD² + 4²
or, 80 - 16 = BD²
so, BD² = 64
so, BD = 8
