求和:1-2+3-4+5………+(2n-1)-2n=

问题描述:

求和:1-2+3-4+5………+(2n-1)-2n=
求和:1-2+3-4+5………+(2n-1)-2n=

=(1-2)+(3-4)+.+(2n-1-2n)=-n对吧,赶紧好评啊