求1+3+5+7+9+…+2n-3+2n-1的值

问题描述:

求1+3+5+7+9+…+2n-3+2n-1的值

(1+2n-1)×(2n-1)÷2÷2
=2n×(2n-1)÷4
=(4n²-2n)÷4
=n²-n/2