Tham khảo Căn_bậc_hai

  1. ↑ Gel'fand, p. 120
  2. ↑ Zill, Dennis G.; Shanahan, Patrick (2008). A First Course in Complex Analysis With Applications (ấn bản 2). Jones & Bartlett Learning. tr. 78. ISBN 0-7637-5772-1.  Extract of page 78
  3. ↑ Parkhurst, David F. (2006). Introduction to Applied Mathematics for Environmental Science. Springer. tr. 241. ISBN 9780387342283. 
  4. ↑ Solow, Anita E. (1993). Learning by Discovery: A Lab Manual for Calculus. Cambridge University Press. tr. 48. ISBN 9780883850831. 
  5. ↑ Heath, Sir Thomas L. (1921). A History of Greek Mathematics, Vol. 2. Oxford: Clarendon Press. tr. 323–324. 
  6. ↑ Muller, Jean-Mic (2006). Elementary functions: algorithms and implementation. Springer. tr. 92–93. ISBN 0-8176-4372-9. , Chapter 5, p 92