1/(1×3)+1/(3×5)+……+1/(9×11)
=1/2×(1-1/3)+1/2×(1/3-1/5)+……+1/2×(1/9-1/11)
=1/2×(1-1/3+1/3-1/5+……+1/9-1/11)
=1/2×(1-1/11)
=1/2×10/11
=5/11
明白请采纳,
有新问题请求助,