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Tentukan apakah deret berikut merupakan deret yang konvergen atau divergen. Berikan penjelasan Saudara.

sum_(n=1)^(oo)((-1)^(n)n)/(n^(2)+3n+5)

Tentukan apakah deret berikut merupakan deret yang konvergen atau divergen. Berikan penjelasan Saudara.\newlinen=1(1)nnn2+3n+5 \sum_{n=1}^{\infty} \frac{(-1)^{n} n}{n^{2}+3 n+5}

Full solution

Q. Tentukan apakah deret berikut merupakan deret yang konvergen atau divergen. Berikan penjelasan Saudara.\newlinen=1(1)nnn2+3n+5 \sum_{n=1}^{\infty} \frac{(-1)^{n} n}{n^{2}+3 n+5}
  1. Check Conditions for Convergence: Use the Alternating Series Test to determine convergence.\newlineAn alternating series ((1)nan)\sum((-1)^n \cdot a_n) converges if the following conditions are met:\newline11. an+1ana_{n+1} \leq a_n for all nn\newline22. limnan=0\lim_{n\to\infty} a_n = 0
  2. Compare ana_n and an+1a_{n+1}: Check the first condition by comparing ana_n and an+1a_{n+1}.
    an=nn2+3n+5a_n = \frac{n}{n^2 + 3n + 5}
    an+1=n+1(n+1)2+3(n+1)+5a_{n+1} = \frac{n+1}{(n+1)^2 + 3(n+1) + 5}
    We need to show that an+1ana_{n+1} \leq a_n for all nn.
  3. Simplify an+1a_{n+1}: Simplify an+1a_{n+1}.an+1=n+1n2+2n+1+3n+3+5=n+1n2+5n+9a_{n+1} = \frac{n+1}{n^2 + 2n + 1 + 3n + 3 + 5} = \frac{n+1}{n^2 + 5n + 9}
  4. Comparison of ana_n and an+1a_{n+1}: Compare ana_n and an+1a_{n+1}. For n1n \geq 1, the denominator of an+1a_{n+1} is larger than the denominator of ana_n, so an+1ana_{n+1} \leq a_n.
  5. Find Limit of ana_n: Check the second condition by finding the limit of ana_n as nn approaches infinity.\newlinelimnnn2+3n+5\lim_{n\to\infty} \frac{n}{n^2 + 3n + 5}\newlineUse L'Hôpital's Rule or observe that the degree of the polynomial in the denominator is higher than the numerator, so the limit is 00.
  6. Series Convergence: Since both conditions of the Alternating Series Test are met, the series converges.

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