Ta có: \( A = \overline {abc} ; B = \overline {abcabc}\)
Xét \(A.7.11.13\)\(=\overline {abc}. 7 . 11 . 13= \overline {abc} . 1001 \)\(=\overline{abc}.(1000+1)\)\(=\overline{abc}.1000+\overline{abc}= \overline {abcabc} \)
Hay \(\overline{abc}.7.11.13=\overline{abcabc}\)
Suy ra: \(\overline {abcabc} :7:11:13 = \overline {abc} \)
Hay \(B:7:11:13=A.\)
