Today’s download provides analytic solutions to polynomial equations up to fourth order (that is quadratic, cubic and quartic equations) and an iterative method to solve equations of higher order.  All these functions are found in the download file:
http://interactiveds.com.au/software/Polynomial.zip

The links below describe these functions in more detail.  Several of the earlier links refer to other download files, but all of the functions are now included in the Polynomial.xlsb spreadsheet.

Solving cubic and quartic equations with Excel
Evaluating Polynomial Functions
Complex Numbers and Solving Quartic Polynomial Equations
Solving higher order polynomials
Evaluating higher order polynomials …
Polynomial Update

EvalPoly Function

Quadratic, Cubic, CubicC and Quartic functions

RPolyJT function used to solve a 60th order polynomial

Bottom of the input and output for the same function