Write the Word or Phrase That Best Completes Each Statement $$\csc ^ { 4 } x - \cot ^ { 4 } x = \csc ^ { 2 } x + \cot ^ { 2 } x$$

Essay

Write the word or phrase that best completes each statement or answers the question.
Establish the identity.
- $$\csc ^ { 4 } x - \cot ^ { 4 } x = \csc ^ { 2 } x + \cot ^ { 2 } x$$