Abstract
Inspired by Ramanujan’s unusual approximations for the perimeter of an ellipse with semiaxis 1 and \(r\in \left( 0,1\right) \), a family of approximations of Ramanujan type is constructed. We find the sharp lower and upper approximations have very high accuracy, and better than some known ones.
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Acknowledgements
This work was supported by the Fundamental Research Funds for the Central Universities (No. 2015ZD29) and the National Natural Science Foundation of China (No. 61672205).
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Tian, JF., Yang, Z., Ha, MH. et al. A family of high order approximations of Ramanujan type for perimeter of an ellipse. RACSAM 115, 85 (2021). https://doi.org/10.1007/s13398-021-01021-7
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DOI: https://doi.org/10.1007/s13398-021-01021-7
Keywords
- Perimeter of an ellipse
- Ramanujan type approximation
- Complete integral of the second kind
- Monotonicity
- Inequality