9514 1404 393
Answer:
AD = 37.77 m
Step-by-step explanation:
Your premise is incorrect. Angle ECD is about 42.88°, found using the law of cosines.
∠ECD = arccos((EC²+DC²-ED²)/(2·EC·DC))
∠ECD = arccos(765/1044) ≈42.88°
The rest of the work is correct:
AC = AB×sin(81°)/sin(42.88°) ≈ 66.77 m
AD = AC - DC = 66.77 m - 29 m
AD ≈ 37.77 m
