Đáp án: A=2mu2021-2
A chia het cho 5 va A chia het cho 10
chu so tan cung la:
3mu21=......3
8mu104=.....6
127mu50=.......9
409mu100=......1.
Giải thích các bước giải: Co: 2A=2mu 2+2mu3+2mu4+.....+2mu2021
⇒2A-A=2mu2021-2
A=2mu2021-2
2mu2021-2=2mu4 × 505 ×2-2
=......6 ×2-2=....2-2=...0
ma ........0 chia het cho 5 va chia het cho 10.Vay A chia het cho 5 va chia het cho 10.
Co: 3mu21=3mu4 ×5 ×3
=......1 ×3=......3
8mu104=8mu4 ×26=........6
127mu50=127mu4 ×12 ×127mu2
=.......1 ×......9=.......9
409mu100=409mu4 ×25
=.............1