Write the word or phrase that best completes each statement or answers the question. Use mathematical induction to prove the statement is true for all positive integers n. -6 + 12 +

Write the word or phrase that best completes each statement or answers the question.
Use mathematical induction to prove the statement is true for all positive integers n.
-6 + 12 + 18 + … + 6n = 3n(n + 1)