Question

A blue boat and a red boat are on the same side of a lake and are 18 miles apart. The blue boat is 30 miles from a lighthouse on the opposite side of the lake. The angle formed by the boats and the lighthouse, and whose vertex is at the blue boat, measures 120°. Find the distance from the red boat to the lighthouse. What is the angle made from the lighthouse to the two boats?

Answer 1

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Answer:

• red boat distance: 42 miles
• angle at lighthouse: 22°

Explanation:

The Law of Cosines can be used to find the distance from the red boat to the lighthouse.

b² = l² +r² -2lr·cos(B)

b² = 18² +30² +2·18·30·cos(120°) = 1764

b = √1764 = 42

The distance from the red boat to the lighthouse is 42 miles.

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The angle at the lighthouse can be found using the law of sines.

sin(L)/l = sin(B)/b

L = arcsin(l/b·sin(B)) = arcsin(18/42·sin(120°)) ≈ 21.79°

The angle between the boats measured at the lighthouse is about 22°.