Thay `x=2021` vào A: `A=2020.2021-2022 .2021^2 +2021^3=-2021`
x=2021⇒2020=x-1; 2022=x+1, thay vào A ta có:
A=2020x-2022x2+x3
=(x-1)x-(x+1)x2+x3
=x2-x-x3-x2+x3
=x
=2021
x=2021⇒2020=x-1; 2022=x+1, thay vào A ta có:
A=2020x-2022x2+x3
=(x-1)x-(x+1)x2+x3
=x2-x-x3-x2+x3
=-x
=-2021
Có: A = 2020.2021 - 2022.20212 + 20213
= 2020.2021 - 20212.(2022 - 2021)
= 2020.2021 - 20212
= 2021.(2020 - 2021)
= 2021.(-1)
= -2021
Thay x=2021 vào A, ta được:
\(A=2020\cdot2021-2022\cdot2021^2+2021^3\)
=-2021
