Town B is on a bearing of 116° from town A. Town C is on a bearing 204° from town B. Town C isdue south and 23 km from town A. Find the distance of town B from town C. Give your answers to 3significant figures.[1]2. Sine and Cosine RulesName: Class: Date:Copyright Mathster.com 2014. Licensed by Your School with permission to redistribute
Question
Town B is on a bearing of 116° from town A. Town C is on a bearing 204° from town B. Town C isdue south and 23 km from town A. Find the distance of town B from town C. Give your answers to 3significant figures.[1]2. Sine and Cosine RulesName: Class: Date:Copyright Mathster.com 2014. Licensed by Your School with permission to redistribute
Solution
To solve this problem, we need to use trigonometry and the sine and cosine rules. Let's break it down step by step.
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Understanding the Bearings and Positions:
- Town B is on a bearing of 116° from town A.
- Town C is on a bearing of 204° from town B.
- Town C is due south and 23 km from town A.
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Visualizing the Problem:
- Draw a diagram with town A at the origin.
- Draw a line from A to B at an angle of 116° from the north.
- Draw a line from B to C at an angle of 204° from the north.
- Draw a vertical line from A to C, which is 23 km.
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Finding the Angles:
- The bearing of 116° from A to B means the angle between the north direction and line AB is 116°.
- The bearing of 204° from B to C means the angle between the north direction and line BC is 204°.
- Since town C is due south of town A, the angle between the north direction and line AC is 180°.
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Calculating the Angle at Town B:
- The angle between line AB and line AC is 116° - 180° = -64° (which is equivalent to 296° in a positive direction).
- The angle between line BC and line AC is 204° - 180° = 24°.
- Therefore, the angle at town B (angle ABC) is 180° - 24° = 156°.
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Using the Sine Rule:
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We need to find the distance BC.
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In triangle ABC, we know:
- Angle BAC = 116°
- Angle ABC = 156°
- Side AC = 23 km
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Using the sine rule:
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Solving for BC:
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Calculate the sines:
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Substitute these values into the sine rule:
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Solve for BC:
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Therefore, the distance of town B from town C is approximately 49.9 km to 3 significant figures.
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