Great Falls is at approximately 47.5 degrees N, and 111.3 degrees W. Lemhi is approximately 45.5 degrees N, and 113.5 degrees W. (We will assume the rivers flow straight from Great Falls to Lemhi on the surface of Earth). Apply the Law of Cosines for Sides of a spherical triangle to find the angle between Great Falls and Lemhi.

The angle between Great Falls and Lemhi is approximately 3.02°

Step-by-step explanation:

The location parameters are;

The Great Falls location = 47.5° N, 111.3° W

The location of Lemhi = 45.5 °N and 113.5 °W

Therefore, we have;

The angle between the Great Falls and the poles, AP = 90° - 47.5° = 42.5°

The angle between Lemhi and the poles, PB = 90° - 45.5° = 44.5°

The angle between the lines of longitude, P = 113.5° - 113° = 0.5°

By the law of cosines for Sides of a spherical triangle, we have;

CosAB = cos AP·cosPB + sinAP·sinPB·cosP

Where;

AB = The angle between Great Falls and Lemhi

∴ CosAB = cos(47.5°) × cos(44.5°) + sin(47.5°) × sin(44.5°) × cos(0.5°) ≈ 0.9986

AB ≈ arccos(0.9986) ≈ 3.02°

The angle between Great Falls and Lemhi ≈ 3.02°

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step-by-step explanation: