Ta có: abcdeg¯¯¯¯¯¯¯¯¯¯¯¯¯¯=ab0000¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯+cd00¯¯¯¯¯¯¯¯¯¯+eg¯¯¯¯¯abcdeg¯=ab0000¯+cd00¯+eg¯
=ab¯¯¯¯¯.10000+cd¯¯¯¯¯.100+eg¯¯¯¯¯=ab¯.10000+cd¯.100+eg¯
=ab¯¯¯¯¯.9999+ab¯¯¯¯¯+cd¯¯¯¯¯.99+cd¯¯¯¯¯+eg¯¯¯¯¯=ab¯.9999+ab¯+cd¯.99+cd¯+eg¯
=ab¯¯¯¯¯.11.909+ab¯¯¯¯¯+cd¯¯¯¯¯.11.9+cd¯¯¯¯¯+eg¯¯¯¯¯=ab¯.11.909+ab¯+cd¯.11.9+cd¯+eg¯
=11.(ab¯¯¯¯¯.909+cd¯¯¯¯¯.99)+(ab¯¯¯¯¯+cd¯¯¯¯¯+eg¯¯¯¯¯)=11.(ab¯.909+cd¯.99)+(ab¯+cd¯+eg¯)
Vì 11.(ab¯¯¯¯¯.909+cd¯¯¯¯¯.99)⋮1111.(ab¯.909+cd¯.99)⋮11 và ab¯¯¯¯¯+cd¯¯¯¯¯+eg¯¯¯¯¯⋮11ab¯+cd¯+eg¯⋮11 nên abcdeg¯¯¯¯¯¯¯¯¯¯¯¯¯¯⋮11abcdeg¯⋮11