Unit 6.1: Reciprocal, Quotient, and Pythagorean Theorem Video URL
https://youtu.be/hPblMh_cX9A
Unit 6.2: Sum, Difference, and Double-Angle Identity
https://youtu.be/VX9aKEXM5zg
Unit 6.3: Proving Identities
https://youtu.be/bW1bAvsydi4
Unit 6.4: Solving Trigonometric Equations using Identities
https://youtu.be/1xKo1Bqgv38
