bn=1/(2n-1)(2n+1),数列bn的前n项和为Bn,求证,Bn
问题描述：
bn=1/(2n-1)(2n+1),数列bn的前n项和为Bn,求证,Bn
答
Bn=1/1*1/3+1/3*1/5+.+1/(2n-1)(2n+1)
=1/2*{（1-1/3）+1/3-1/5+.1/(2n-1)-1/(2n+1)}
=1/2*{1-1/(2n+1)}
=1/2*2n/(2n+1)
因为2n/(2n+1)所以Bn