求数列1x2,2x2²,3x2的三次方,4x2的四次方,…,nx2(的n次方),…的前n项和Sn

问题描述:

求数列1x2,2x2²,3x2的三次方,4x2的四次方,…,nx2(的n次方),…的前n项和Sn

UUK

Sn =1x2+2x2²+3x2的三次方+4x2的四次方+…+nx2(的n次方)2Sn =1x2²+2x2的三次方+3x2的四次方+…+nx2(的n+1次方)两式相减得Sn =-[2+2²+2的三次方+2的四次方+…+2(的n次方)]+nx2(的n+1次方)注意到2+2&su...