## Reflection: Self-Talk Sum and Difference Day 1 of 2 - Section 3: Finding the other sum and difference formulas

This lesson was a struggle for students.  I was not able to pinpoint the exact cause but I feel many factor came into play.

The first may be that the proofs done by the students were not the same as the video. I am considering giving students a diagram similar to the one on the video for them to use to find the cos (A+B) and then move to the algebra for sin (A-B) cos (A-B) and the tangent formulas.

Another reason may be that students have not done many algebra proofs. This is due to the fact that most of these students were in a curriculum that was prior to Common Core and algebra proof was not a emphasized. If this is the case I should see better results in the future.

For my first class I had them write sin(A+B) instead of sin (u+v). I felt the students struggled since the parameters were the same in the formula and the problem.  To alleviate this issue I change the formula sheet to sin(u+v).

This did help some students but the majority still struggled with the proofs.  I will have to spend more time analyzing the students understanding as we progress with these properties.

Struggle for students
Self-Talk: Struggle for students

# Sum and Difference Day 1 of 2

Unit 9: Trigonometric Identities
Lesson 9 of 14

## Big Idea: After analyzing a proof for the sum of angles sine formula, students work to produce the other sum and difference formulas.

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Standards:
Subject(s):
Math, Trigonometric identities, sum and difference formulas
70 minutes

### Katharine Sparks

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