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  1. #include <iostream>
  2. #include <math.h>
  3. using namespace std;
  4.  
  5. int main() {
  6. 	int n, a=1, as=a, b=1;
  7. 	double S=0.0, u=2.0;
  8. 	cin >> n;
  9. 	for(int i=1, k=2; i<=n; i++, k++)
  10. 	{
  11. 		a=3*b+2*a;
  12. 		b=2*as+b;
  13. 		u*=(2.0/k);
  14. 		S+=u*(1.0/(1+a*a+b*b));
  15. 		as=a;			//запоминание переменной а
  16. 	}
  17. 	printf("%7lf", S);
  18. 	return 0;
  19. }
Success #stdin #stdout 0s 3300KB
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0.059734
https://ideone.com/FaMs0g
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
secret

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