`17 xx 2`
`= ( 10 + 7) xx2`
`= 10 xx 2 + 7 xx 2`
`= 20 + 14`
`= 34`
---------------------------
`99 xx 9`
`= (90 + 9) xx9`
`= 90 xx 9 + 9 xx 9`
`= 810 + 81`
`= 891`
---------------------------
`10 xx 10`
= `100`
---------------------------
`200 xx 2000`
`= 400 000`
-----------------------------
`1778xx54`
`= 1778 xx ( 50 + 4)`
`= 1778 xx 50 + 1778 xx 4`
`= 88900 + 7112`
`= 96012`
-------------------------------
`90xx34`
`= 90 xx ( 30 + 4)`
`= 90 xx 30 + 90 xx 4`
`= 2700 + 360`
`= 3060`
---------------------------
`56xx78`
`= (50 + 6) xx 78`
`= 50 xx 78 + 78 xx 6`
`= 3900 + 468`
`= 4368`
-------------------------------------------------------------------
`text{Rút gọn lại kết quả bài làm :}`
`17 xx 2= 34`
`99 xx 9 = 891`
`10 xx 10 = 100`
`200 xx 2 000 = 400 000`
`1778 xx 54 = 96012`
`90 xx 34 = 3060`
`56 xx 78 =4368`
