Tính tổng sau: 2021+2022+...+2029
Giải thích
2021+2022+2023+2024+2025+2026+2027+2028+2029
=2021+2029+2022+2028+2023+2027+2024+2026+2025
=5000+5000+5000+5000+2500 =22500
2021+2022+2023+2024+2025+2026+2027+2028+2029
=2021+2029+2022+2028+2023+2027+2024+2026+2025
=5000+5000+5000+5000+2500 =22500