Write the Word or Phrase That Best Completes Each Statement $$\frac { \cos x } { \sec x - 1 } - \frac { \cos x } { \sec x + 1 } = \frac { 2 \cos x } { \tan ^ { 2 } x }$$

Essay

Write the word or phrase that best completes each statement or answers the question.
Establish the identity.
- $$\frac { \cos x } { \sec x - 1 } - \frac { \cos x } { \sec x + 1 } = \frac { 2 \cos x } { \tan ^ { 2 } x }$$