a1=1/1-1/3
a2=1/2-1/4
a3=1/3-1/5
a4=1/4-1/6
a5=1/5-1/7
a6=1/6-1/8
a7=1/7-1/9
a8=1/8-1/10
a9=1/9-1/11
a10=1/10-1/12
∴S10=a1+a2+a3+...+a10
=1/1+1/2-1/11-1/12 (中间全部抵消 )
=175/132
a1=1/1-1/3
a2=1/2-1/4
a3=1/3-1/5
a4=1/4-1/6
a5=1/5-1/7
a6=1/6-1/8
a7=1/7-1/9
a8=1/8-1/10
a9=1/9-1/11
a10=1/10-1/12
∴S10=a1+a2+a3+...+a10
=1/1+1/2-1/11-1/12 (中间全部抵消 )
=175/132