电线跨度中三次方程的计算方法

在电线跨度的计算中常会遇到实系数三次方程求根问题，通常是先求一个实根，然后从方程中去掉一个因子，得到一个二次因子，再用求根公式求二个共轭复根或两个实根。本文提出一种直接求二次因子的迭代方法。还给出这种迭代方法一个可以简单地直接验证的收敛性定理。

The Third Equation Calculation Method of the Cable Span

We. often meet with real number third equation and root finding in cable span calculation,the normal practice is to find a real root,then eliminate a factor from the equation,obtaining a second factor,again,use the finding loot formula to find two conjugate complex roots or two real roots,This paper put forward an iteration method of finding second factor,also gives a convergent theorem which can simply demonstrate the iteration method.