Example 5

9.1.5 Example 5

Description

Quick Overview

This section presents a problem involving the relationship between the height of a tower and the lengths of its shadow at different sun altitudes.

Standard

In Example 5, a problem is solved that involves calculating the height of a tower based on the lengths of its shadow when the sun is at different altitudes. Two right triangles are used to set up equations based on the tangent function.

Detailed

Detailed Summary

Example 5 deals with a geometric problem surrounding a tower's height and the length of its shadow under two different angles of elevation of the sun (30° and 60°). The solution involves using trigonometric principles, specifically the tangent function, to relate the height of the tower (AB) to the lengths of its shadows (BC and BD) at the specified angles. The relationship established shows that the shadow length at 30° is 40 meters longer than that at 60°, leading to the formulation of two equations based on right triangles formed in the diagram. The mathematical approach culminates in determining that the height of the tower is 20√3 meters.

Key Concepts

  • Height of a Tower: The vertical distance from the base of the tower to its top.

  • Shadow Length: The distance from the base of the object (the tower) to the tip of its shadow.

  • Angles of Elevation: The angles formed with the horizontal line to the line of sight to the top of the tower, measured at 30° and 60° in this case.

  • Trigonometric Functions: Functions such as tangent that relate angles to ratios of sides in triangles.

Memory Aids

🎵 Rhymes Time

  • When the sun is high and shadows low, the tower's height will surely show.

📖 Fascinating Stories

  • Imagine a brave knight measuring tower heights with a magic shadow stick that grows as the sun bows lower in the sky.

🧠 Other Memory Gems

  • Remember HATS: Height = Adjacent × Tangent of Angle for shadow problems.

🎯 Super Acronyms

SHAD = Shadow Height at Different angles.

Examples

  • Example 1: If a person stands 10 m away from a tree that is 5 m tall, what is the angle of elevation to the top of the tree?

  • Example 2: A flagpole casts a shadow of length 15 m when the angle of elevation is 45°. What is the height of the flagpole?

Glossary of Terms

  • Term: Angle of Elevation

    Definition:

    The angle formed between the horizontal line and the line of sight to an object above the horizontal.

  • Term: Tangent Function

    Definition:

    A trigonometric function that relates the angle of a right triangle to the ratio of the length of the opposite side to the length of the adjacent side.

  • Term: Right Triangle

    Definition:

    A triangle where one angle is exactly 90 degrees.

  • Term: Shadow Length

    Definition:

    The length of the projection of an object, like a tower, cast on the ground due to light, such as sunlight.

  • Term: Trigonometric Relationship

    Definition:

    Relationships among the angles and sides of triangles.