2020ⅹ2021一2019ⅹ2022如何速算与巧算？

Question

如题所述

Answer 1

设2020为a，则原算式可以写为：
a×(a+1)-(a-1)×(a+2)
=a²+a-(a²-a+2a-2)
=a²+a-a²-a+2
=2

Answer 2

2020ⅹ2021一2019ⅹ2022
=2020x(2020+1) -（2020-1)(2020+2)
=2020²+2020-2020²+2020-2020x2+2
【前5项抵消】
=2

Answer 3

2020ⅹ2021一2019ⅹ2022
=（2019+1）ⅹ2021一2019ⅹ2022
=2019ⅹ2021+1ⅹ2021一2019ⅹ2022
=2019ⅹ（2021-2022）+2021
=2021-2019
=2

Answer 4

2019×2021+2021―2019×2022
＝2019×（2021―2022）+2021
＝―2019+2021
＝2

Answer 5

2020*2021-2020*2022+2022
=2028(2021-2022)+2022
=2020*(-1)+2022
=2022-2020=2+