5. (a) A bus is on the opposite side of the road from a building. The distance between the foot of the building and the bus is 20 m. The angle of depression to the bus as observed from the top of the building is 45°. Find the height of the building.



Answer :

Certainly! Let's tackle this problem step-by-step.

1. Understand the given information:
- The distance between the foot of the building and the bus is 20 meters.
- The angle of depression from the top of the building to the bus is 45°.

2. Visualize the problem:
- Imagine you're standing on top of the building looking down. The line of sight from the top to the bus forms the angle of depression with the horizontal line (imagine a line parallel to the ground starting from your eye level).

3. Relate the angle of depression to the angle of elevation:
- The angle of depression from the top of the building to the bus equals the angle of elevation from the bus to the top of the building. Both are 45° because they are alternate interior angles.

4. Set up a right triangle:
- The foot of the building, the bus, and the top of the building form a right triangle.
- The horizontal leg of the triangle is the distance between the foot of the building and the bus (20 meters).
- The vertical leg is the height of the building, which we need to find.
- The angle of elevation (or depression) is 45°.

5. Use trigonometric ratios:
- In a right triangle, the tangent of an angle is the ratio of the opposite side to the adjacent side. Here, for the 45° angle:
[tex]\[ \tan(45°) = \frac{\text{height of the building}}{\text{distance to the building}} \][/tex]

6. Substitute the known values:
- [tex]\[ \tan(45°) = \frac{\text{height of the building}}{20} \][/tex]

7. Recall the value of [tex]\(\tan(45°)\)[/tex]:
- [tex]\[ \tan(45°) = 1 \][/tex]

8. Set up the equation:
- [tex]\[ 1 = \frac{\text{height of the building}}{20} \][/tex]

9. Solve for the height of the building:
- To find the height, isolate the variable:
[tex]\[ \text{height of the building} = 1 \times 20 \][/tex]
[tex]\[ \text{height of the building} = 20 \text{ meters} \][/tex]

10. Conclusion:
- The height of the building is 20 meters.

Note: All calculations agree with the original trigonometric values and the logic used in solving such right-angle triangle problems.