CMR: 42/20x24+42/24x28+...+42/76/80<1
tinh nhanh
( - 42 ) - ( 3 + 42 )
Bo dau ngoac roi tinh
(27+65)+(346-27-65)
(42-69+17)-(42+17)
tinh giùm cái A= 1/2+ 1/6 + 1/12 + 1/12 + 1/30 + 1/42 + 1/42 + 1/56 + 1/72
bo dau ngoac roi tinh: a) (27+65)+(346-27-65) ;b)(42-69+17)-(42+17)
Tinh nhanh
c) 8.19 – 42.(- 19) + 38.5
tinh nhanh
39.(19-13)-19.(39-13)
(42-69+17)-(42+17)
137.(-26)+26.137
-67.11
65.(-21)
tinh nhanh :
\((135-35).(-37)+37.[(-42)-58]\)
tinh nhanh (13+25)+(24-13-42-25)