1. Precal D – Section 8.1 Angles of elevation and depression
Solving Trig Problems
Precal D – Section 8.1
Angles of elevation and depression

2. Angle of Elevation and Depression
Imagine you are standing here.
The angle of elevation is measured from the horizontal up to the object.

3. Angle of Elevation and Depression
The angle of depression is measured from the horizontal down to the object.
A second similar triangle may also be formed.
Constructing a right triangle, we are able to use trig to solve the triangle.

4. Angle of Elevation and Depression
Example #1

5. Angle of Elevation and Depression
Suppose the angle of depression from a lighthouse to a sailboat is 5.7o. If the lighthouse is 150 ft tall, how far away is the sailboat?
5.7o
150 ft.
5.7o x
Construct a triangle and label the known parts. Use a variable for the unknown value.

6. Angle of Elevation and Depression
Suppose the angle of depression from a lighthouse to a sailboat is 5.7o. If the lighthouse is 150 ft tall, how far away is the sailboat?
5.7o
150 ft.
5.7o x
Set up an equation and solve.

7. Angle of Elevation and Depression
150 ft.
5.7o
Remember to use degree mode! x
x is approximately 1,503 ft.

8. Angle of Elevation and Depression
Example #2

9. Angle of Elevation and Depression
A spire sits on top of the top floor of a building. From a point 500 ft. from the base of a building, the angle of elevation to the top floor of the building is 35o. The angle of elevation to the top of the spire is 38o. How tall is the spire?
Construct the required triangles and label.
38o
35o
500 ft.

10. Angle of Elevation and Depression
Write an equation and solve.
Total height (t) = building height (b) + spire height (s)
Solve for the spire height. s t
Total Height b
38o
35o
500 ft.

11. Angle of Elevation and Depression
Write an equation and solve.
Building Height s t b
38o
35o
500 ft.

12. Angle of Elevation and Depression
Write an equation and solve.
Total height (t) = building height (b) + spire height (s) s t b
The height of the spire is approximately 41 feet.
38o
35o
500 ft.

13. Angle of Elevation and Depression
Example #3

14. Angle of Elevation and Depression
A hiker measures the angle of elevation to a mountain peak in the distance at 28o. Moving 1,500 ft closer on a level surface, the angle of elevation is measured to be 29o. How much higher is the mountain peak than the hiker?
Construct a diagram and label.
1st measurement 28o.
2nd measurement 1,500 ft closer is 29o.

15. Angle of Elevation and Depression
Adding labels to the diagram, we need to find h.
h ft
29o
28o
1500 ft
x ft
Write an equation for each triangle. Remember, we can only solve right triangles. The base of the triangle with an angle of 28o is x.

16. Angle of Elevation and Depression
Now we have two equations with two variables. Solve by substitution.
Solve each equation for h.
Substitute.

17. Angle of Elevation and Depression
Solve for x. Distribute.
Get the x’s on one side and factor out the x.
Divide.
x = 35,291 ft.

18. Angle of Elevation and Depression
x = 35,291 ft.
However, we were to find the height of the mountain. Use one of the equations solved for “h” to solve for the height.
The height of the mountain above the hiker is 19,562 ft.

19. Angle of Elevation and Depression
Start homework on a new page. Assignment 8.1 p. 516 #1, 4, 6, 9, 11, 14, 18, 22, 23, 29, 32, 38, 39, 42, 46, 50, 51, 58
Remember to change your calculator between radians and degrees when required.