Ta có : 1 - 2 + 3 - 4 + 5 - 6 + 7 - 8 + ... + 2019 - 2020
= ( 1 - 2) + ( 3 - 4 )+ ( 5 - 6 ) + ( 7 - 8 ) + ... + ( 2019 - 2020)
= ( - 1 ) + ( -1 ) + ( - 1 ) + ( - 1 ) + .... + ( - 1 )
\---------------------------------------------------------------/
có tất cả 1010 số ( - 1 )
= ( - 1 ) . 1010
= ( - 1010 )
Tính
A = 1 - 2 + 3 - 4 + 5 - 6 + 7 - 8 + 9 - ........... + 2019
B = 1 + 2 - 3 + 4 - 5 + 6 - 7 + .............. + 2017 + 2018 - 2019 + 2020
1 - 2 + 3 - 4 + 5 - 6 + 7 - 8 + ..... + 2019 - 2020 + 2021
1-2+3-4+5-6+7-8+...+2019-2020+2021
a) 5+3.(-7)+4:(-2)
b)1-2-3+4+5-6-7+8.....+2017-2018-2019+2020+2021
1+2-3-4+5-6-7-8+...-2019-2020+2021+2022
1+2-3-4+5+6-7-8-....-2019-2020+2021+2022 help
tính nhanh: (1+3+5+7+...+2019+2021)-(2+4+6+8+...+2020)
1-2-3+4+5×6-7+8+...+2017-2018-2019+2020
1-2-3+4+5-6-7+8+...+2018-2019-2020+2021+2022-2023
