\(A=2020\cdot2018-2019^2\)

\(\Leftrightarrow A=\left(2019+1\right)\left(2019-1\right)-2019^2\)

\(\Leftrightarrow A=2019^2-1-2019^2\)

\(\Leftrightarrow A=-1\)

À, cái này là dùng hằng đẳng thức của lớp 8 á ^^

Học tốt!!!

#Bo

\(\frac{-1}{3}:\frac{-5}{6}=\frac{-1}{3}\times\frac{-6}{5}=\frac{2}{5}\)

@muối

(-1/3) : (-5/6) = 2/5

a) 313 + 687 +414 =1000+414=1414

b) 16.87.127=176784

c) 86.34+121.66+35.34=34.(86+35)+121.66=34.121+121.66=121.(34+66)=121.100=12100

d) 68.75+34.50=2.34.75+34.50=34.150+34.50=34.(150+50)=34.200=6800

Câu 1:

2.25 - 24: 2^3

= 50 - 24 : 8

= 50 - 3

= 47

Câu 2:

|-110| - 54 + (-110) - (-12)

= 110 - 54 - 110 + 12

= (110 - 110) - (54 - 12)

= 0 - 42

= - 42

a) 1 - 5 + 9 - 13 + .... + 393 - 397

  = ( 1 - 5 ) + ( 9 - 13 ) + ... + ( 393 - 397 )

  = ( -4 ) + ( -4 ) + ... + ( -4 )

  = ( -4 ) x 197

  = -788

b) - 2 + 4 - 6 + 8 - ... - 238 + 240

   = ( -2 + 4 ) + ( -6 + 8 ) + ... + ( -238 + 240 )

   = 2 + 2 + ... + 2

   = 2 x 60

   = 140

Cảm ơn nha!!!
 

1954 - 2 . ( 2019 + 977 ) + ( 4038 - 5421 ) + 4421.

= 1954 - 4038+ 1954 + 4038 - 5421 + 4421

= 1954 + 1954 - 421 + 421 + 5000 + 4000

= 2. 1945 + 9000

=3908

xl mik chưa lm xong

45.69-32.(-45)

=45.69+32.45

=45.(69+32)

=45.101

=4545

-41(59+2)+59(41-2)

=-41.61+59.39

=-2501+2301

=-200

45 . 69 - 32 . ( -45 ) 

= 45 . 69 + 32 . 45

= 45 . ( 69 + 32 )

= 45 . 101

= 45 . ( 100 + 1 )

= 45 . 100 + 45

= 4500 + 45

=4545