“Although Cardan reduced his particular equations to forms lacking a term in x^2, it was Vieta who began with the general form{{center/s}}x^3 + px^2 + qx + r = 0{{center/e}}and made the substitution x = y -\frac{1}{3}p, thus reducing the equation to the form{{center/s}}y^3 + 3by = 2c.{{center/e}}He then made the substitution{{center/s}}z^3 + yz = b,   or   y = \frac{b - z^2}{z},{{center/e}}which led to the form{{center/s}}z^6 + 2cz^2 = b^2,{{center/e}}a sextic which he solved as a quadratic.”