Math Problem Statement

Find the first five terms of the sequence a sub n=((-1)^n+1)(n-1/2n+1).

Solution

Let's find the first five terms of the sequence given by the formula:

an=((1)n+1)(n12n+1)a_n = \left((-1)^n + 1\right) \left(\frac{n - \frac{1}{2}}{n + 1}\right)

We will calculate each term a1,a2,a3,a4,a5a_1, a_2, a_3, a_4, a_5 by substituting n=1,2,3,4,5n = 1, 2, 3, 4, 5 into the formula:

  1. For n=1n = 1:

a1=((1)1+1)(1121+1)=(1+1)(122)=0×14=0a_1 = \left((-1)^1 + 1\right) \left(\frac{1 - \frac{1}{2}}{1 + 1}\right) = \left(-1 + 1\right) \left(\frac{\frac{1}{2}}{2}\right) = 0 \times \frac{1}{4} = 0

  1. For n=2n = 2:

a2=((1)2+1)(2122+1)=(1+1)(323)=2×36=2×12=1a_2 = \left((-1)^2 + 1\right) \left(\frac{2 - \frac{1}{2}}{2 + 1}\right) = \left(1 + 1\right) \left(\frac{\frac{3}{2}}{3}\right) = 2 \times \frac{3}{6} = 2 \times \frac{1}{2} = 1

  1. For n=3n = 3:

a3=((1)3+1)(3123+1)=(1+1)(524)=0×58=0a_3 = \left((-1)^3 + 1\right) \left(\frac{3 - \frac{1}{2}}{3 + 1}\right) = \left(-1 + 1\right) \left(\frac{\frac{5}{2}}{4}\right) = 0 \times \frac{5}{8} = 0

  1. For n=4n = 4:

a4=((1)4+1)(4124+1)=(1+1)(725)=2×710=1410=1.4a_4 = \left((-1)^4 + 1\right) \left(\frac{4 - \frac{1}{2}}{4 + 1}\right) = \left(1 + 1\right) \left(\frac{\frac{7}{2}}{5}\right) = 2 \times \frac{7}{10} = \frac{14}{10} = 1.4

  1. For n=5n = 5:

a5=((1)5+1)(5125+1)=(1+1)(926)=0×912=0a_5 = \left((-1)^5 + 1\right) \left(\frac{5 - \frac{1}{2}}{5 + 1}\right) = \left(-1 + 1\right) \left(\frac{\frac{9}{2}}{6}\right) = 0 \times \frac{9}{12} = 0

First Five Terms:

The first five terms of the sequence are:

a1=0,a2=1,a3=0,a4=1.4,a5=0a_1 = 0, \quad a_2 = 1, \quad a_3 = 0, \quad a_4 = 1.4, \quad a_5 = 0

Would you like further details or have any questions?


Related Questions:

  1. What pattern do you notice in the sequence's terms as nn increases?
  2. How would the sequence change if (1)n+1(-1)^n + 1 were replaced by (1)n+1+1(-1)^{n+1} + 1?
  3. Can this sequence be related to any known mathematical series?
  4. What is the behavior of the sequence as nn approaches infinity?
  5. How would the sequence change if the denominator of the fraction inside the sequence formula were n1n-1 instead of n+1n+1?

Tip: Notice how sequences with alternating terms (involving (1)n(-1)^n) often produce terms that either cancel out or follow a repeating pattern. This can be useful in predicting future terms without direct computation.

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Math Problem Analysis

Mathematical Concepts

Sequences
Alternating Series

Formulas

Sequence formula: $a_n = \left((-1)^n + 1\right) \left(\frac{n - \frac{1}{2}}{n + 1}\right)$

Theorems

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Suitable Grade Level

Advanced High School