Sum of Infinite Series: Find 1/sqrt(2)

In summary, the conversation is about finding the sum of an infinite series and the question asker is struggling to use the ratio test to get the desired result of 1/sqrt(2). They suspect it may involve a power series and someone suggests comparing it to the power series for cos(x) in order to get the desired result.
  • #1
Umar
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Hey guys! I just have a question regarding finding the sum of an infinite series. Attached is the image of the question. I've tried to use the ratio test but it doesn't give me the result I need which happens to be 1/sqrt(2). I feel like this is one of those power series questions, but I'm not quite sure how to deal with this. If anyone could help out, that would be greatly appreciated!

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  • #2
Umar said:
Hey guys! I just have a question regarding finding the sum of an infinite series. Attached is the image of the question. I've tried to use the ratio test but it doesn't give me the result I need which happens to be 1/sqrt(2). I feel like this is one of those power series questions, but I'm not quite sure how to deal with this. If anyone could help out, that would be greatly appreciated!
This is just the power series expansion for $\cos\frac\pi4.$
 
  • #3
This is [tex]\sum_{n=0}^\infty \frac{(-1)^n}{(2n)!}\left(\frac{\pi}{4}\right)^{2n}[/tex]

Compare that to the power series for cos(x), [tex]\sum_{n=0}^\infty \frac{(-1)^n}{(2n)!}x^{2n}[/tex] to get Opalg's result.
 
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1. What is the formula for finding the sum of infinite series for 1/sqrt(2)?

The formula for finding the sum of infinite series for 1/sqrt(2) is S = a/(1-r), where "a" is the first term in the series (in this case, 1/sqrt(2)) and "r" is the common ratio (in this case, 1/2).

2. Can the sum of infinite series for 1/sqrt(2) be calculated without using the formula?

Yes, it can be calculated using the partial sum formula S_n = a(1-r^n)/(1-r), where "n" is the number of terms in the series. However, this method requires an understanding of limits and may not be feasible for larger values of "n".

3. What is the limit of the sum of infinite series for 1/sqrt(2)?

The limit of the sum of infinite series for 1/sqrt(2) is 2, meaning that as the number of terms in the series approaches infinity, the sum will converge to 2.

4. How do you know if the sum of infinite series for 1/sqrt(2) is convergent or divergent?

The sum of infinite series for 1/sqrt(2) is convergent because the common ratio (1/2) is less than 1, which is a necessary condition for convergence. Additionally, the limit of the series is a finite number (2) rather than approaching infinity, further confirming convergence.

5. Can the sum of infinite series for 1/sqrt(2) be used in real-world applications?

Yes, the sum of infinite series for 1/sqrt(2) can be used in various real-world applications such as in physics, engineering, and finance. It can be used to calculate the total cost of an investment with compound interest, the total distance traveled by an object under constant acceleration, and more.

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