1. Introduction
Several mathematicians have tried to solve general polynomial equations of
degree higher than four with the techniques similar to that applied to solve
cubics and quartics. However they didn't succeed. In 1770 Lagrange showed
that these equations couldn't be solved with such methods. Later Paolo
Ruffini (1799), Abel (1826), and Galois (1832), proved more rigorously
that it is impossible to solve the general polynomial equations of degree ¯ve
and above in radicals. With certain conditions imposed on the coe±cients(or equivalently on the roots), these equations become solvable in radicals, and are
aptly named solvable equations ([1], [2]).
In this paper we present a method to solve a septic equation which has the
property that the sum of its four roots is equal to the sum of its remaining three
roots. In the method proposed here the septic equation is ¯rst converted to an
octic equation by adding a root; the octic is then decomposed into two quartic
polynomials in a novel fashion. The quartic polynomial factors are equated to
zero and solved to obtain the seven roots of the given septic along with the
added root. In the next section we describe the decomposition method, and
in the further sections we discuss the behavior of roots and the conditions for
the coe±cients. In the last section a numerical example is solved using the
proposed method.