\(1-2+3-4+5-6+...+2019-2020+2021\)
\(=\left(1+3+5+....+2021\right)-\left(2+4+6+...+2020\right)\)
\(=\left(\frac{\left(2021+1\right).1011}{2}\right)-\left(\frac{\left(2020+2\right).1010}{2}\right)\)
\(=\frac{2022.1011}{2}-\frac{2022.1010}{2}=\frac{2022}{2}=1011\)
...
Ra mỗi kết quả:
-1011
1-2+3-4+5-6+...+2019-2020+2021
1 - 2 + 3 - 4 + 5 - 6 + 7 - 8 + ..... + 2019 - 2020 + 2021
1-2+3-4+5-6+7-8+...+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)
Câu 30. Giá trị của tổng
S =1+ 2 - 3 - 4 + 5 + 6 - 7 - 8 + 9 +10 -... + 2018 - 2019 - 2020 + 2021 là
A. 2020 . B. 2021. C. 1. D. -1.
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+6-7-7+...+2018-2019-2020+2021
