Verify Identities Problems, math homework help

1. Which of the following identities would be the best option to use to verify the identity below?

2. What would be the best next step for verifying the identity?

3. Which of the following would be the best first step for verifying the identity below?

4. What would be the best next step for verifying the identity below?

5. What would be the best next step for verifying the identity below?

6. What would be the best first step for verifying the identity below?

7. The following expression was simplified incorrectly. In which line was an error first made when simplifying the identity shown below?