# Discovering Trig Identities (Day 3 of 4)

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## Objective

SWBAT visualize and interpret the trigonometric identities with a focus today on the co-function identities.

#### Big Idea

Students use TI-Nspire calculators to develop their own understandings of what trigonometric identities are and why they work.

3 minutes

The Warm Up question asks students to recall an algebraic identity. Obviously, there are the standard algebraic identities (like binomial expansion), but most of my students will not come up with those. It is important for students to continue to reflect on the concept of an identity: what makes an identity an identity (MP7). At this point, I expect that my students will apply their working knowledge of identities, recall some examples, and make up some identities, for example x+x=2x.

Teacher's Note:  My intention is that each of my students will complete this lesson using their own calculator. It is important that students are able to see the calculator clearly. The lessons works best when students can work through the problems at their own pace. However, I would encourage open communication within teams. I encourage my students to ask each other for help with the calculator and to seek clarification on questions if they are unsure.

20 minutes

## Closure

7 minutes

As a closure to today’s lesson have students complete the third page in their Trig Identities book with the co-function identities. I ran this similar to yesterday’s lesson. I facilitated a whole class discussion of the findings by having students raise their hands to share their answers. Then, I clearly wrote out the co-function identities on the board to ensure all students are copying them correctly.

If students still don’t seem to be grasping the co-function identities and I have sufficient time remaining in the period, I will ask my students to find the sine of a 60 degree angle and the cosine of a 30 degree angle using a special triangle. This practice will help to solidify student understanding of the identities covered in today's lesson (MP2).

Finally, I had students attempt the last question on the flipchart. Again, this is just a preview question. In my classes, many students were not able to answer it correctly. I plan to address these missed preview questions on day 5 after our discovery of the trig identities is complete.

## Homework

Today I will assign Trig Equations Homework 2.

Or here is a word version if you prefer to edit anything: Trig Equations Homework 2.