To find the length ab of a small lake, a surrounding veyor measured angle acb to 96, ac to be 91 yards, and bc to be 71 yards. what is the approximate length of the lake?

Using the law of Cosins that states: For any triangle, a, b and c are sides and C is the angle opposite side c
c² = a² + b² − 2ab cos(C)

Applying this in our problem, we get:
 AB²= 71²+91²- 2x91x71 cos96
AB²=14627.7 yard²
AB=121 yard