Write the Word or Phrase That Best Completes Each Statement $$\tan ^ { 2 } u ( 1 + \cos 2 u ) = 1 - \cos 2 u$$

Essay

Write the word or phrase that best completes each statement or answers the question.
- $$\tan ^ { 2 } u ( 1 + \cos 2 u ) = 1 - \cos 2 u$$