Question

三分之一乘以五加五分之一乘以七.加二千零一乘以二千零三

Answer 1

1/(3*5)=1/2(1/3-1/5)

1/(5*7)=1/2(1/5-1/7)

1/(2001*2003)=1/2(1/2001-1/2003)

原式=1/2(1/3-1/5+1/5-1/7+……+1/2001-1/2003)

=1/2(1/3-1/2003)=1001/6009