想你啦
春芽
共回答了20个问题采纳率:100% 举报
a1+a2+.+a100
=1/(1*3)+1/(3*5)+1/(5*7)+.+1/(199*201)
=1/2×(1-1/3)+1/2×(1/3-1/5)+1/2×(1/5-1/7)+1/2×(1/7-1/9)+.+1/2×(1/199-1/201)
=1/2×(1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11+.+1/197-1/199+1/199-1/201)
=1/2×(1-1/201)
=1/2×(201/201-1/201)
=1/2×200/201
=100/201
希望对你有所帮助~~~
1年前
6