1+2+3+4+5…(2n-1)=
问题描述:
1+2+3+4+5…(2n-1)=
答
=【1+(2n-1)]*(2n-2)/2+[(2n-1)+1]/2
=2n*(n-1)+n
=2n^2-2n+n
=2n^2-n