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Sia

伊莎白's Question
Math
Posted 7 months ago

X\boldsymbol{X} Incorrect.

The series converges by the alternating series test. How many terms give a partial sum, SnS_{n}, within 0.02 of the sum, SS, of the series?
n=1(1)n1nn
\begin{array}{l}
\sum_{n=1}^{\infty} \frac{(-1)^{n-1}}{n} \\
n \geq
\end{array}

i 50
eTextbook and Media

Hint
Assistance Used

Since the series converges and is an alternating series of the form n=1(1)n1an\sum_{n=1}^{\infty}(-1)^{n-1} a_{n}, by Theorem 9.9: Error Bounds for Alternating Series you know SSn<an+1\left|S-S_{n}\right|<a_{n+1}.
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Answer from Sia
Posted 7 months ago
Solution by Steps
step 1
To determine the number of terms needed to get a partial sum within 0.02 of the total sum of the series, we use the error bound for alternating series. According to Theorem 9.9, for an alternating series of the form n=1(1)n1an \sum_{n=1}^{\infty}(-1)^{n-1} a_{n} , the error SSn \left|S - S_{n}\right| is less than an+1 a_{n+1}
step 2
The given series is n=1(1)n1n \sum_{n=1}^{\infty} \frac{(-1)^{n-1}}{n} . Here, an=1n a_{n} = \frac{1}{n}
step 3
To find the number of terms n n such that the error is within 0.02, we need an+1<0.02 a_{n+1} < 0.02
step 4
Since an+1=1n+1 a_{n+1} = \frac{1}{n+1} , we set up the inequality 1n+1<0.02 \frac{1}{n+1} < 0.02
step 5
Solving for n n , we get n+1>50 n+1 > 50 , which simplifies to n>49 n > 49
step 6
Therefore, we need at least 50 terms to ensure the partial sum is within 0.02 of the total sum
Answer
50
Key Concept
Error Bound for Alternating Series
Explanation
The error bound for an alternating series states that the absolute error is less than the next term in the series. By ensuring the next term is less than the desired error margin, we can determine the number of terms needed.

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