求极限:lim(x→0)[cosx+cos^x+cos3(次方)x+……+cosn(次方)x] /(cosx-1),[n(n+1)]/2,

问题描述:

求极限:lim(x→0)[cosx+cos^x+cos3(次方)x+……+cosn(次方)x] /(cosx-1),[n(n+1)]/2,