Question

1+3+5+7+9+11+···+[4m-3]+[4m-1]=___

Answer 1

　　一共有（4m-1-1)/2 +1=2m项-------（位数-首数）除以公差+1
　　(1+4m-1)+(3+4m-3)+……+（2m-1+2m+1) ------共m项
=4m+4m+……4m
=4m²

Answer 2

1+5+9+···++[4m-3]+3+7+11+···+[4m-1]=[m(1+4m-3)]/2+[m(3+4m-1)]/2
=m(4m-2)/2+m(4m-2)/2=m(4m-2)=4m^2-2m