Math Problem Statement

To find the height of a flagpole, a student stands a random distance away from it and measures the angle ofelevation from her feet to the top of the flagpole to be 70o. The student then moves 2m further away from the flagpole in the same line of sight as before, and notices that the new angle of elevationas measured before isnow60o. Draw a diagram depicting the situation, then calculate the height of the flagpole

Solution

To solve this problem, we'll use trigonometry, specifically the tangent function, which relates the angle of elevation to the height and distance of the object. Let's break down the steps and draw the diagram.

Step 1: Draw the Diagram

  1. Draw a vertical line representing the flagpole with height hh.
  2. Mark two points on the ground along the same line of sight:
    • The first point AA, where the student is initially standing, is a distance xx away from the base of the flagpole.
    • The second point BB, where the student moves 2 meters further away, is a distance x+2x + 2 from the base of the flagpole.
  3. Draw the horizontal ground line connecting the base of the flagpole to both points AA and BB.
  4. Draw two lines from points AA and BB to the top of the flagpole, forming angles of elevation 7070^\circ and 6060^\circ respectively.

This will create two right triangles, ABC\triangle ABC and ABD\triangle ABD, where:

  • hh is the height of the flagpole,
  • xx is the distance from the flagpole to point AA,
  • x+2x + 2 is the distance from the flagpole to point BB,
  • θ1=70\theta_1 = 70^\circ (angle of elevation from point AA),
  • θ2=60\theta_2 = 60^\circ (angle of elevation from point BB).

Step 2: Set Up Equations Using Tangent

For the first position (at point AA): tan(70)=hx\tan(70^\circ) = \frac{h}{x} So, h=xtan(70)h = x \cdot \tan(70^\circ)

For the second position (at point BB): tan(60)=hx+2\tan(60^\circ) = \frac{h}{x + 2} So, h=(x+2)tan(60)h = (x + 2) \cdot \tan(60^\circ)

Step 3: Set Up the Equation to Solve for xx and hh

Since both expressions represent the height hh, we can set them equal to each other: xtan(70)=(x+2)tan(60)x \cdot \tan(70^\circ) = (x + 2) \cdot \tan(60^\circ)

Expanding and solving for xx: xtan(70)=xtan(60)+2tan(60)x \cdot \tan(70^\circ) = x \cdot \tan(60^\circ) + 2 \cdot \tan(60^\circ) x(tan(70)tan(60))=2tan(60)x \cdot (\tan(70^\circ) - \tan(60^\circ)) = 2 \cdot \tan(60^\circ) x=2tan(60)tan(70)tan(60)x = \frac{2 \cdot \tan(60^\circ)}{\tan(70^\circ) - \tan(60^\circ)}

Step 4: Calculate xx and then hh

Substituting the values of the tangents: tan(70)2.747\tan(70^\circ) \approx 2.747 tan(60)1.732\tan(60^\circ) \approx 1.732

x=21.7322.7471.732x = \frac{2 \cdot 1.732}{2.747 - 1.732} x3.4641.0153.413metersx \approx \frac{3.464}{1.015} \approx 3.413 \, \text{meters}

Now, calculate hh: h=xtan(70)3.4132.7479.374metersh = x \cdot \tan(70^\circ) \approx 3.413 \cdot 2.747 \approx 9.374 \, \text{meters}

Final Answer:

The height of the flagpole is approximately 9.37 meters.


Would you like further details on any part of the solution? Here are some related questions:

  1. What other trigonometric identities could be used to solve similar problems?
  2. How would the problem change if the student moved closer to the flagpole?
  3. Can this method be applied to non-right triangles? How?
  4. How does the accuracy of the angle measurements affect the result?
  5. What if the ground was not level, how would that affect the calculations?

Tip: Always ensure that your calculator is set to the correct mode (degrees/radians) when solving trigonometric problems.

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Angle of Elevation
Tangent Function

Formulas

tan(θ) = opposite / adjacent
h = x * tan(θ1)
h = (x + 2) * tan(θ2)

Theorems

Trigonometric Ratios in Right Triangles

Suitable Grade Level

Grades 10-12