解析几何中求离心率的问题在高考中经常出现 ,其解法较灵活 .下面介绍一些常用的方法 .一、定义法例 1　已知椭圆mx2 + 5 y2 =5m的离心率e =105 ,求m的值 .解　将椭圆方程化为标准方程 ,得x25 + y2m =1.(1)当 0 m 5时 ,∵a2 =5 ,b2 =m ,∴c2 =5 -m ,e=ca =5 -m5 .由e =105 ,? Analytic geometry in the eccentricity problem often occurs in the college entrance examination, the solution is more flexible. Here are some commonly used methods. First, the definition of the law 1 known ellipse mx2 + 5 y2 = 5m eccentricity e = 105, seeking m Values. Solution The elliptic equation is transformed into a standard equation to obtain x25 + y2m = 1. (1) When 0 m5, ∵a2 =5, b2 =m, ∴c2 =5 -m, e=ca =5 -m5 By e =105 ,?