一道数学题，急！！！！！！！！

裂陪慎缓芦模项相消法做孝孙。

1/(1*3)+1/(3*5)+1/(5*7)+~~~+n
=1/2[(1-1/3)+(1/扒闹裤3-1/5)+(1/弯瞎5-1/7)+~~~+1/春简(2n-1)-1/(2n+1)]
=1/2[1-1/3+1/3-1/5+1/5-1/7+~~~+1/(2n-1)-1/(2n+1)]

=1/2[1-1/(2n+1)]
=1/2[1-1/(2n+1)]
=n/(2n+1)

1/(1*3)+1/(3*5)+1/(5*7)+~~~+1/（n-1）n
=1/2（1-1/3+1/3-1/5+1/5-1/7+……-1/信升燃山(n-1)+1/(n-1)-1/滑段老n）
=1/2(1-1/n)
=(n-1)/2n

题最喊枯亮败中后一项应该是1/（2n-1）(2n+1)
原式=(1-1/3)+(1/3-1/5)+(1/5-1/7)+……+[1/(2n-1)-1/郑宽(2n+1)]
=1-1/(2n+1)
=2n/(2n+1)

1/如此绝配(1*3)+1/(3*5)+1/(5*7)+...+ 1/(n-2)*n
=0.5* (1/1 - 1/3 + 1/3 -1/5 +1/渣宏迅5 -1/7 +...-1/n)
=0.5*(1-1/n)

1/(1*3)+1/(3*5)+1/(5*7)+……+1/源如悉(2n-1)(2n+1)
=(1/2)*(1-1/橡隐3)+(1/雹乎2)*(1/3-1/5)+……+（1/2)*[1/(2n+1) -1/(2N-1)]
=(1/2)*[1-1/(2n-1)]
=1/2-1/(4n-2)