提取公因式有:
(qre/(2πε0))*(1/(r-re/2)^3-1/(r+re)^3)
对第二项通分为:
(3rer^2+(re^3)/4)/(r^2-re^4/4)^3
忽略高于re的高次项re^2.re^4
就有:
3rer^2/r^6
结合公因子就有图片上答案了.
提取公因式有:
(qre/(2πε0))*(1/(r-re/2)^3-1/(r+re)^3)
对第二项通分为:
(3rer^2+(re^3)/4)/(r^2-re^4/4)^3
忽略高于re的高次项re^2.re^4
就有:
3rer^2/r^6
结合公因子就有图片上答案了.