Proving a trig identity might just be easier than proving your own identity at the airport. Learners first investigate a table of values to determine and prove the addition formulas for sine and cosine. They then use this result to develop the subtraction formulas.

Concepts

trigonometric identities, proofs

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Additional Tags

math

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Instructional Ideas

• Use the resource to introduce addition and subtraction formulas for sine and cosine

Classroom Considerations

• Learners need to have graphing calculators available
• Note that some portions of the lesson are likely to take more than the indicated time allotment
• The 18th installment of a 19-part series

Pros

• Resource indicates where to look for mathematical practices
• Proofs have scaffolding with fill-in-the-blank statements

Cons

• None

Common Core

HSF-TF.C.8 HSF-TF.C.9 MP8