`1/4 +x=5/2xx8/7`

`=> 1/4 + x= 40/14`

`=> 1/4 + x= 20/7`

`=> x= 20/7-1/4`

`=>x=73/28`

1/4 + x = 20/7

x = 20/7 - 1/4 

x = 73/28 

vậy x = 73/28

3+2+2+2.8-1+4.1

=3+2+2+16-1+4

=(3+2+2-1)+(16+4)

=(5+2-1)+20

=(7-1)+20

=6+20

=26

ai giúp mik với ak mik cần gấp

\(\dfrac{1}{1.4}+\dfrac{1}{4.2}+\dfrac{1}{2.8}+\dfrac{1}{8.4}+\dfrac{1}{4.16}+\dfrac{1}{16.8}\)

= \(\dfrac{1}{4}.\left(1+\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+\dfrac{1}{32}\right)\)

= \(\dfrac{1}{4}.\left(\dfrac{3}{2}+\dfrac{3}{8}+\dfrac{3}{32}\right)\)

= \(\dfrac{1}{4}.\dfrac{3}{2}\left(1+\dfrac{1}{4}+\dfrac{1}{16}\right)\)

= \(\dfrac{1}{4}.\dfrac{3}{2}\left(\dfrac{16}{16}+\dfrac{4}{16}+\dfrac{1}{16}\right)\)

= \(\dfrac{3}{8}.\dfrac{21}{16}\)

= \(\dfrac{63}{128}\)

a) 2 x 4 và 2 x 8 

2 x 4 = 8

2 x 8 = 16

=> 2 x 4 < 2 x 8

Dễ ẹc:

a) 2 x 4 = 8

2 x 8 = 16

Mà 8 < 16

=> 2 x 4 < 2 x 8

b) 2 x 9 = 18

2 x 2 = 4

Mà 18 > 4

=> 2 x 9 > 2 x 2

c) 2 + 2 x 2 = 2 + 4 = 6

2 x 8 + 9 = 16 + 9 = 25

Mà 6 < 25

=> 2 + 2 x 2 < 2 x 8 + 9

7 x 8 - 2 x 8 - 4 - 56 x 4 

=49 - 16 - 4 - 224

=  - 195

tchs mk tchs lại

7 x 8 - 2 x 8 - 4 - 56 x 4 = -195

5 + 2 x 8/21 : 2/5

= 5 + 16/21 x 5/2

= 5 + 40/21

= 105/21 + 40/21

= 145/21