a, A = 123 x 123 và 121 x 124

             15129     >     15004

Và  123 x 123 lớn hơn  121x124  125 đơn vị

k cho mik nha

mik đang rất rất rất rất cần điểm

\(\dfrac{x+1}{124}+1+\dfrac{x+2}{123}+1=\dfrac{x+3}{122}+1+\dfrac{x+4}{121}+1\)

\(\Leftrightarrow\dfrac{x+125}{124}+\dfrac{x+125}{123}=\dfrac{x+125}{122}+\dfrac{x+125}{121}\)

\(\Leftrightarrow\left(x+125\right)\left(\dfrac{1}{124}+\dfrac{1}{123}-\dfrac{1}{122}-\dfrac{1}{121}\ne0\right)=0\Leftrightarrow x=-125\)

<=>\(\dfrac{x+1}{124}+\dfrac{x+2}{123}-\dfrac{x+3}{122}-\dfrac{x+4}{121}=0\)

<=>\(\left(\dfrac{x+1}{124}+1\right)+\left(\dfrac{x+2}{123}+1\right)-\left(\dfrac{x+3}{122}+1\right)-\left(\dfrac{x+4}{121}+1\right)=0\)

<=>\(\dfrac{x+125}{124}+\dfrac{x+125}{123}-\dfrac{x+125}{122}-\dfrac{x+125}{121}=0\)

<=>\(\left(x+125\right)\left(\dfrac{1}{124}+\dfrac{1}{123}-\dfrac{1}{122}-\dfrac{1}{121}\right)=0\)

<=>x+125=0

<=>x=-125

a) B = 124 x 122 = (123+1) x (123-1) = 123 x 123 -123 + 123 -1 = A -1

=> B < A

b) B = 986 x 985 = (987-1) x (984+1) = 987 x 984 + 987 - 984 -1 = A +2

=> B > A

a) Ta có: A = 123 x 123 = 123 x ( 124 - 1 ) = 123 x 124 - 123
               B = 121 x 124 = ( 123 - 2 ) x 124 = 123 x 124 - 248
Suy ra: 123 x 124 - 123 > 123 x 124 - 248 hay A > B

b) Ta có: C = 123 x 137137 = 123 x 137 x 1001 = 137 x 123 x 1001
               D = 137 x 123123 = 137 x 123 x 1001
Suy ra: C = D

c) Ta có: E = 2015 x 2017 = 2015 x ( 2016 + 1 ) = 2015 x 2016 + 2015
               F = 2016 x 2016 = ( 2015 + 1 ) x 2016 = 2015 x 2016 + 2016
Suy ra: 2015 x 2016 + 2015 < 2015 x 2016 + 2016 hay E < F 
 

a) `123 - 27 + 27 + 13 - 123`

`= (123 - 123) + (27 - 27) + 13`

`= 0 + 0 + 13`

`= 13`

`---`

b) `175 + 25 + 13 + 15 - 175 - 25`

`= (175-175)+(25-25)+25+13`

`=0+0+25+13`

`=28`

`---`

c) \(53\times39+47\times39+53\times21+47\times21\)

\(=\text{[}\left(53+47\right)\times39]+\left[\left(53+47\right)\times21\right]\)

\(=\left(100\times39\right)+\left(100\times21\right)\)

\(=3900+2100\)

`=6000`

`---`

d) \(49\times35+49\times16-49\times61\)

`=` \(49\times\left(35+16-61\right)\)

`=` \(49\times\left(-10\right)\)

`=-490`

A =   1 − 1 2 . 1 − 1 3 . 1 − 1 4 ... 1 − 1 19 . 1 − 1 20 A = 1 2 . 2 3 . 3 4 .... 18 19 . 19 20 A = 1 20 > 1 21

Vậy A> 1 21

vì 123<124=> 123/124<1

vì 1435>1433=>1435/1433>1

=>1435/1433>123/124

=>-1435/1433<-123/124