(1)1/x-1/(x+1)=(x+1-x)/(x(x+1))=1/(x(x+1))(2)1/x(x+1)+1/(X+1)(x+2)+...+1/(x+999)(x+1000) =1/x-1/(x+1)+1/(x+1)-1/(x+2)+……+1/(x+999)-1/(x+1000) =1/x-1/(x+1000) =(x+1000-x)/(x(x+1000)) =1000/(x(x+1000))