（一的平方减二分之一的平方）乘（一的平方减三分之一的平方）乘（一的平方减四分之一的平方）乘…

(1^2-(1/2)^2)*(1^2-(1/3)^2)*(1^2-(1/4)^2)*……*(1^2-(1/100)^2
=(1-1/2)(1-1/3)……(1-1/100)(1+1/2)(1+1/3)……(1+1/100)
=1/2.2/3.3/4.98/99.99/100.3/2.4/3.99/98.101/100
/前后两两配对相消
=1/2.2/3.3/2.3/4.4/3.98/99.99/98.101/100
=1/2.101/100
=101/200
.代表乘以