Example

Example: First Five Terms of an=(1)nn3a_n = (-1)^n n^3

Find the first five terms of the sequence whose general term is an=(1)nn3a_n = (-1)^n n^3 by substituting n=1,2,3,4,5n = 1, 2, 3, 4, 5:

  • a1=(1)113=1a_1 = (-1)^1 \cdot 1^3 = -1
  • a2=(1)223=8a_2 = (-1)^2 \cdot 2^3 = 8
  • a3=(1)333=27a_3 = (-1)^3 \cdot 3^3 = -27
  • a4=(1)443=64a_4 = (-1)^4 \cdot 4^3 = 64
  • a5=(1)553=125a_5 = (-1)^5 \cdot 5^3 = -125

The first five terms are 1,8,27,64,125-1, 8, -27, 64, -125. The (1)n(-1)^n factor causes the signs to alternate, while n3n^3 cubes each position number.

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Updated 2026-05-26

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Ch.12 Sequences, Series and Binomial Theorem - Intermediate Algebra @ OpenStax

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