tim abcd biet abcd-abc-ab-a=2086
abcd-abc-ab-a=2086
1000a+100b+10c+d-100a-10b-c-10a-b-a=2086
(1000a-100a-a)+(100b-10b-b)+(10c-c)+d=2086
899a+89b+9c+d=2086
=>abcd=2323
abcd-abc-ab-a = 2086
1000a+100b+10c+d-100a-10b-c-10a-b-a = 2086
889a + 89b + 9c + d = 2086
đến đây chịu