1.nx(n/n+1)= n-(n/n+1)
2.1x1/2=1-1/2,2x2/3=2-2/3,3x3/4=3-3/4,……
(1-1/2)/10x(2-2/3)/9x(3-3/4)/8x.x(10-10/11)/1
=(1x1/2)/10x(2x2/3)/9x(3x3/4)/8x.x(10x10/11)/1
=10/11=(1/2)/10x(4/3)/9x(9/4)/8x.....x(100/11)/1=((1/2)x(1/10))x((4/3)x(1/9))x((9/4)x(1/8))x.....x(100/11) (注意约分）=10/11