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### Course: Class 11 Math (India) - Hindi > Unit 3

Lesson 4: Trigonometric identities: Sum and difference- Review of trig addition identities (Hindi)
- Using the cosine angle addition identity (Hindi)
- Using trig addition identities finding sides (Hindi)
- Using the trig angle addition identities
- Proof of the sine addition identity (Hindi)
- Proof of the cosine angle addition identity (Hindi)
- Using the cosine double angle identity (Hindi)

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# Review of trig addition identities (Hindi)

Lets review all the different trigonometric angle addition identities: sin(a+b), sin(a-c), cos(a+b), cos(a-b), cos(2a), and sin(2a).