Write the Word or Phrase That Best Completes Each Statement $2 + 5 + 8 + \ldots + ( 3 n - 1 ) = \frac { n } { 2 } ( 3 n + 1 )$

Essay

Write the word or phrase that best completes each statement or answers the question.
Use mathematical induction to prove the following statement for all positive integers n.
- $2 + 5 + 8 + \ldots + ( 3 n - 1 ) = \frac { n } { 2 } ( 3 n + 1 )$