Tính giá trị biểu thức sau
( $\frac{2}{2020}$ +$\frac{3}{2019}$ +...+$\frac{2021}{1}$ )( $\frac{1}{2021}$ + $\frac{2}{2020}$ +...+ $\frac{2020}{2}$ ) - ( $\frac{1}{2021}$ + $\frac{2}{2020}$ +...+ $\frac{2021}{1}$ )( $\frac{2}{2020}$+$\frac{3}{2019}$ +...+$\frac{2020}{2}$)
Vote 5*+CTLHN