a)29.(19-13)-19.(29-13) b)31.(-18)+31.(-81)-31 c)13.(23+22)-3.(17+28) d)-48+48.(-78)+48.21

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1. Giải thích các bước giải:

   a)29.(19-13)-19.(29-13)

   =29.19-29.13-19.29-19.13

   =(29.19-29.19)-(29.13-19.13)

   =0-13.(29-19)

   =(-13).10=-130

   b)31.(-18)+31.(-81)-31

   =31.[-18+(-81)-1]

   =31.(-100)=-3100

   c)13.(23+22)-3.(17+28)

   =13.45-3.45

   =45.(13-3)

   =45.10=450

   d)-48+48.(-78)+48.21

   =48.(-1)+48.(-78)+48.21

   =48.[-1+(-78)+21]

   =48.(-58)=2784

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2. Bạn tham khảo :

   $a,$

   $29.(19 – 13) – 19.(29 – 13)$ 

   $= 29 . 19 – 29 .13 – 19 . 29 –  19.13$

   $= 29(19 – 13 – 19)- 247$

   $= 29 . (-13) – 247$

   $= -377 – 247$

   $= -624$

   $b,$

   $31.(-18)+31.(-81)-31$
   $=31.[ -18 + (-81) – 1]$

   $=31 . (-100)$

   $= -3100$

   $c,$

   $13.(23+22)-3.(17+28)$

   $= 13 . 45 – 3. 45$

   $= 45 (13 – 3)$

   $= 45.10$

   $= 450$ 

   $d,$

   $-48+48.(-78)+48.21$

   $= 48 . (-1) + 48 . (-78)+ 48.21$

   $= 48.[ (-1) + (-78) + 21)$

   $= 48 . -58$

   $= 2784$

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