Reflection: Staircase of Complexity If sin(A) = 3/5, what is sin(2A)? - Section 2: Share

When we had our class discussion I decided to start with the calculator strategy since it was so prevalent among students in the class. Almost every group started with that strategy. During the discussion I purposely rounded my angle measure to the nearest tenth so that students could see that I would not get the exact answer that way.

There were no groups that could derive the double angle formula on their own, but the key was rewriting sin(2A) as sin(A + A). Once I wrote that on the board I heard a chorus of "a-has" and students understood exactly how to find this value from yesterday's sum and difference formulas.

Staircase of Complexity: Sequence of Discussion

If sin(A) = 3/5, what is sin(2A)?

Unit 5: Trigonometric Relationships
Lesson 5 of 15

Big Idea: How do the double angle formulas follow from the sum and difference formulas?

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50 minutes

Tim Marley

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