Question

(1/2+1/3.+1/2009)*(1+1/2+1/3..+1/2008)-(1+1/2+1/3..+1/2009)*

Answer 1

上式=(1/2+1/3.+1/2009)+(1/2+1/3.+1/2009)*(1/2+1/3..+1/2008)-(1/2+1/3..+1/2008)-(1/2+1/3.+1/2009)*(1/2+1/3..+1/2008)=1/2009