Problem 1 · Analytic geometry and trigonometry
Two sides of a triangular parcel measure 120 m and 85 m, and the angle between them is 72°. The length of the third side is most nearly:
- A.47.2 m
- B.123.8 m
- C.167.1 m
- D.203.4 m
Show the answer and solution
Answer: B: 123.8 m
Law of cosines: c² = 120² + 85² − 2(120)(85)cos 72° = 14,400 + 7,225 − 6,304 = 15,321 m², so c = 123.8 m. Adding the 2ab cos C term gives 167.1 m, and evaluating cos 72 in radian mode gives 203.4 m.
Analytic geometry and trigonometry · Reference Handbook: Mathematics
