[1] Gerard P. Michon, www.numericana.com/answer/ellipse.htm
[2] Gerald B. Folland, Real Analysis, Modern Techniques And Their Applications,
John Wiley And Sons, Second Edition.
[3] W. Rudin, Principles of Mathematical Analysis, McGraw-Hill, Third Edition
[4] George B. Thomas, Ross L. Finney Calculus And Analytic Geometry, Addison-
Wesley, Ninth Edition.