Tính A=1/x(x+1)+1/(x+1)(x+2)+....+1/(x+2019)(x+2020)

A=1x(x+1)+1(x+1)(x+2)+...+1(x+2019)(x+2020)    =1x−1x+1+1x+1−1x+2+....+1x+2019−1x+2020   =1x−1x+2020   =x+2020x(x+2020)−xx(x+2020)   =2020x(x+2020)Vậy    A=2020x(x+2020)