1.2/(1*3)+2/(3*5)+2/(5*7)+……+2/(9*11)
=1-1/3+1/3-1/5+1/5-1/7+……+1/9-1/11
=1-1/11
=10/11
2. 1/(1*3)+1/(3*5)+1/(5*7)+……+1/(97*99)
=1/2[1-1/3+1/3-1/5+1/5-1/7+……+1/97/-1/99]
= 1/2[1-1/99]
=1/2*98/99
=49/99
3.1-(5/6)+(7/12)-（9/20）+（11/30）-（13/42）+（15/56）-（17/72）+（19/90）
=1-(1/2+1/3)+(1/3+1/4)-(1/4+1/5)+(1/5+1/6)-(1/6+1/7)+(1/7+1/8)-
（1/8+1/9)+(1/9+1/10)
=1/2+1/10
=6/10
=3/5
4.(88888888*88888888)/(1+2+3+4+5+6+7+8+7+6+5+4+3+2+1)
=(11111111*8)^2/[(1+7)*7+8]
=111111111^2*8^2/8^2
=11111111^2