Question

Tính A = 1.4 + 2.5 + 3.6 + ...+ 2022.2025

giúp mik nhanh vs ạ!!

Answer 1

A = 1.4 + 2.5 + 3.6 + ... + 2022.2025
A = 1.(2 + 2) + 2.(3 + 2) + 3.(4 + 2) + ... + 2022.(2023+2)
A = (1.2 + 2.3 + 3.4 + ... + 2022.2023) + (1.2 + 2.2 + 3.2 + ... + 2022.2)
Đặt B = 1.2 + 2.3 + 3.4 + ... + 2022.2023
3B = 1.2.(3-0) + 2.3.(4-1) + 3.4.(5-2) + ... + 2022.2023.(2024-2021)
3B = 1.2.3 - 0.1.2 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 + ... + 2022.2023.2024-2022.2023.2021
3B = 2022.2023.2024=...
B = ...
Tự làm tiếp nha