Cubic Equation on Excel, simple, no iteration or macro.
Only 4 cells input and 1 cell output. These can be put into your own spreadsheet.
You can examine the formulas. Nothing hidden.
Based on Eric Schecter equations on https://math.vanderbilt.edu/schectex/courses/cubic/ 12/4/16.
It either gives a good result or a #NUM! error. I speculate that it is giving the good result when there is one root. That can be useful in many problems. I speculate that it is giving the #NUM! error when there are two or three roots. I speculate this occurs when it must take square roots of negative numbers.