Beacon Lesson Plan Library

You Can't Go Wrong with a Right Triangle 2

Linda Knowles


Students measure objects and solve problems in the real world using the properties of right triangle trigonometry.


Adds, subtracts, multiplies, and divides real numbers, including square roots and exponents using appropriate methods of computing (mental mathematics, paper-and-pencil, calculator).

represents and applies geometric properties and relationships to solve real-world and mathematical problems including ratio, proportion, and properties of right triangle trigonometry.

Interprets data that has been collected, organized, and displayed in charts, tables, plots.


-Paper, pencil, straightedge, graph paper
-Protractor, glue gun, washers, paper clips, string, drinking straws
-Overhead projector and transparencies
-Scientific calculator
-Colored yarn in different lengths (5ft.,10ft., etc.)
-Tape measure


1. Prepare the transparency. (File Document #1)
2. Know the exact measurement of the flagpole of the school. (The fire department of our city measured the flagpole at Gulf Breeze High School.)
3. Collect all of the materials needed .
4. Run off the worksheet for the first day. (File Document #2)
5. Run off the instructions for making the protractor device called an Inclinometer (File Document #3)
6. Prepare a transparency to explain the measuring process. (File Document #4)
7. Run off Cooperative Worker Checklist. (File Document #7)


This lesson is part of a series of lessons entitled You Canít Go Wrong With a Right Triangle I, II, and III

Lesson III is adapted from a lesson originally taught by Charlene Kincaid, Gulf Breeze High School, Santa Rosa District Schools

Prior knowledge required: Students should have a working knowledge of the properties of a right triangle, how to solve an equation and how to use a protractor. This lesson is to follow a lesson on the trigonometric functions of sine, cosine and tangent.
1. Review the properties of a right triangle, the Pythagorean Theorem and solving an equation using basic trigonometric relationships.

2. Use a transparency (File Document #1) to illustrate an example of when a trigonometric relationship will be used to measure distances, such as a distance across a lake.

3. Distribute a worksheet to each student and ask him or her to set up the trigonometric relationship they will use to solve for the unknown quantity. (File Document #2)

4. Circulate around the room and help the students as needed.

5. The students will use their calculators and solve for the unknown in each equation.

6. Collect and grade the worksheet.

7. Review the worksheet from the day before.

8. Students will be placed in groups of three and will make an inclinometer out of a drinking straw, a protractor, a paper clip, string, and hot glue. (Instructions are in File Document #3) They will use this device to measure the angle of elevation from an observation point to the top of the schoolís flagpole.

9. Each group will be given a different length of yarn that will be used to measure from the base of the flagpole.

10. The teacher will give a detailed explanation of the measuring process to the groups. (File Document #4)

11. Students will be put into groups of three to collect the data needed for their calculations. The teacher will accompany them. The groups will work together to collect the data. For instance, one student could measure from the base of the flagpole, two students would calculate the angle of elevation from the observation point to the top of the flagpole and one student could record all calculations, listing what each member of the group did.

12. Students will return to the classroom and transfer their data (distance from the base of the flagpole and angle of elevation) to a piece of graph paper using an appropriate scale. (I.e.1 square = 1 foot, etc.) This is a good place for artwork such as a drawing of the flagpole as a side of the right triangle.

13. Under the drawing on the graph paper, the group should write and solve the trigonometric equation they used to find the desired measurement. On the back of the graph paper they should identify which member of the group did what task., artwork, etc.

14. The teacher will collect and grade each groupís paper.

15. Students will complete cooperative worker checklist.


Assessment will be both formative and summative. Formative assessment will be accomplished daily by observation as the teacher circulates in the classroom monitoring the set up of the equations to be solved. At the end of the first day, the teacher will collect and evaluate the completed worksheets using the rubric provided in File Document #5. Evaluation of the completed graphs using the rubric provided in File Document #6 will complete the assessment of the lesson. Teacher will review Cooperative Learner Checklist and conference with students as needed.

Attached Files

Document showing use of triangle and rubric.     File Extension: pdf

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