..9. M ..9 M ... 9. ( M M ... ).A − A A A − A A   − SO...

99...9. _m 99...9 _m ... 9. ( _{m m} ... ).

a ₋ a a a ₋ a a

   

−

so 9 1 9

m m so

=    +  + +  nên ta đặt bằng ^{9 . k} ( ^{k ∈ Ν} )

a ₋ a