原式=2020×20212021-2020×20202020-1×20202020=2020×(20212021-20202020)-20202020=2020×10001-20202020=0
原式=2020*2021*(10001-10001)
=0
解:
原式=2020×20212021-2021×20202020
=2020×2021×(10001-10001)
=2020×2021×0
=0
2020×20212021-2021×20202020=2020×(20202020+10001)-(2020+1)×20202020=2020×20202020+2020×10001-2020×20202020-20202020=2020×10001-(20200000+2020)=2020×10001-2020×10000-2020=2020×(10001-10000-1)=2020×0=0