Write the Word or Phrase That Best Completes Each Statement $$\text { Explain how to solve } e ^ { 2 x } + 4 e ^ { x } - 21 = 0 \text { analytically. }$$

Essay

Write the word or phrase that best completes each statement or answers the question.
- $$\text { Explain how to solve } e ^ { 2 x } + 4 e ^ { x } - 21 = 0 \text { analytically. }$$