Tính tổng sau đây: C 0 2021 - 2C 1 2021 + 2^2C 2 2021 - 2^3C 3 2021...
Giải thích
C20210−2C20211+22C20212−23C20213+…−22021C20212021
=C20210+C20211−2+C20212−22+C20213−23+…+C20212021−22021
=C2021012021+C2021112020−2+C2021212019−22+C2021312018−23+…+C20212021−22021
=1+−22021=−12021=−1.