Using Trigonometric Ratios (Day 1 of 2)

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SWBAT use trigonometric ratios to solve a right triangle.

Big Idea

Students review basic right triangle trigonometry as a foundation for our next few units.


15 minutes

At the start of class today, students will have their second attempt at the Quick Quiz - Special Triangle. This will be their last opportunity to re-take this quiz during the class period. My Quick Quiz strategy is described in this video: Special Right Triangles, quick quiz closure.

Finding Angles

20 minutes


Today, I will be using pages 1-25 of the Flipchart-Using Trignometric Ratios Day 1 and 2.pdf to help students recall how to find a missing angle in a right triangle. I break down the implementation of this resource in the Using Trigonometric Ratios Video Explanation of Flipchart.

While presenting page 4 of the flipchart, I plan to talk with my students about finding a good method to remember the trig ratios. Of course, memorizing the phrase Soh Cah Toa is a popular way for students to remember the ratios, but I find that some students don’t actually spell it right so it doesn’t really work for them. I am going to encourage my students to make up a phrase that goes with Soh Cah Toa to help them spell is correctly. Maybe something like, some old horse caught another horse taking oats away. (Not appropriate for our students, but this college level acronym made me laugh… some old hippie caught another hippie tripping on acid. Perhaps your students will be just as creative!)

I know pages 6-9 of the flipchart seem very basic. I have found that my students often confuse the opposite and adjacent sides of a triangle, so I emphasize to them that the positions of these angles change based on the reference angle.

In my course, calculator use is encouraged. I plan to use pages 13-16 of the flipchart to introduce how to set up our TI-nSpire calculators to calculate angle measurements in degrees. I will not introduce my students to radian angle measurement until the Trig Functions unit.

Finally I will present pages 17-19 of the flipchart as examples of how to find a missing angle given known information. At this time, I will introduce the concept of inverse trig functions and show my students how to use these functions on their calculators.

Closure: Clicker Checks

15 minutes

To close out today's learning and briefly assess which students have met the learning target, I will ask my students to answer the built in clicker questions on pages 20-25 of the Flipchart-Using Trignometric Ratios Day 1 and 2.


Today, I will assign students Homework 3 - Fundamentals of Trigonometry as homework.

Teaching Note: The last section on this homework has not been covered in class yet. We will be reviewing how to find the missing side lengths tomorrow. So, I will likely give students a couple of days to complete this assignment.