5# = 5 . 4# = 5 . 4 . 3# = 5.4.3.2# = 5.4.3.2.1# = 5.4.3.2.1.0# = 5.4.3.2.1.1 = 120
Vậy 5# = 120.
5# = 5 . 4# = 5 . 4 . 3# = 5.4.3.2# = 5.4.3.2.1# = 5.4.3.2.1.0# = 5.4.3.2.1.1 = 120
Vậy 5# = 120.
5# = 5.[(5 - 1)#] = 5. 4# = 5.4.[(4 - 1)#] = 5.4.3# = 5.4.3[(3 - 1)#] = 5.4.3.2# = 5.4.3.2.[(2 - 1)#] = 5.4.3.2.1# = 5.4.3.2.1.[(1 - 1}#] = 5.4.3.2.1.0# = 5.4.3.2.1.1 = 120
Sao sai được.