故事：
http://www.cskp.org/kpsq/great/tartaglia.htm
程式：
http://wongsircalculator.orgfree.com/Casio50/Cubic%20Equations%201.htm
更多：
http://wenku.baidu.com/view/2fafa0bf960590c69ec37681
http://www.math.cornell.edu/~dwh/courses/M122-S00/supplements/cardano.html