I'd like to know how to solve a cubic and quartic equation by Lagrange's method. In the wiki (http://en.wikipedia.org/wiki/Quadratic_formula#By_Lagrange_resolvents, http://en.wikipedia.org/wiki/Cubic_equation#Lagrange.27s_method, http://en.wikipedia.org/wiki/Quartic_formula#Solving_by_Lagrange_resolvent) there is the method for solve those equations, but, not appears truly a methodical method, appears that in each page the equation are solving of a different way. I'd like of a formula, a step-by-step, for the lagrange's method. You can help me?