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Evaluate.
sum_(n=0)^(oo)n!(cos ((1)/(sqrt(n!)))-1)

Evaluate.\newlinen=0n!(cos1n!1) \sum_{n=0}^{\infty} n !\left(\cos \frac{1}{\sqrt{n !}}-1\right)

Full solution

Q. Evaluate.\newlinen=0n!(cos1n!1) \sum_{n=0}^{\infty} n !\left(\cos \frac{1}{\sqrt{n !}}-1\right)
  1. Find First Term: The series starts at n=0n=0, so let's find the first term. For n=0n=0, the term is 0!(cos(1/0!)1)0!(\cos(1/\sqrt{0!})-1) which is 1(cos(1/1)1)=01(\cos(1/1)-1) = 0.
  2. General Term for n>0: Now, let's consider the general term for n>0. We have n!(cos(1n!)1)n!(\cos(\frac{1}{\sqrt{n!}})-1). Since cos(1)\cos(1) is close to 0.540.54 and decreases as the argument gets smaller, the term cos(1n!)\cos(\frac{1}{\sqrt{n!}}) will approach 11 as nn increases.
  3. Approaching 11: Because cos(1n!)\cos(\frac{1}{\sqrt{n!}}) approaches 11, the expression (cos(1n!)1)\left(\cos\left(\frac{1}{\sqrt{n!}}\right)-1\right) approaches 00. This means that for large nn, the terms of the series become very small.
  4. Factorial Growth vs. Cosine: However, we are multiplying by n!n!, which grows very fast. So we need to check if the factorial growth or the cosine approaching 11 has a stronger effect on the terms.
  5. Factorial Dominance: For large nn, n!n! grows faster than any polynomial function, and since the cosine function is bounded between 1-1 and 11, the factorial will dominate. This means the terms will not approach 00, and the series will diverge.
  6. Series Divergence: Since the series diverges, it does not have a finite sum. Therefore, we cannot calculate the sum of the series as it does not converge to a specific value.

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