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### Course: Trigonometry > Unit 4

Lesson 4: Angle addition identities- Trig angle addition identities
- Using the cosine angle addition identity
- Using the cosine double-angle identity
- Using the trig angle addition identities
- Proof of the sine angle addition identity
- Proof of the cosine angle addition identity
- Proof of the tangent angle sum and difference identities

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# Using the trig angle addition identities

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