Question

还有一题没回答我呢!1乘3分之1+3乘5分之1+5乘7分之1...+（2n-1）（2n+1）分之1等于几,

Answer 1

1乘3分之1+3乘5分之1+5乘7分之1...+（2n-1）（2n+1）分之1

=1/2(1-1/3+1/3-1/5+...+1/2n-1-1/(2n+1)

=1/2(1-1/2n+1)

=n/(2n+1)