7 x 2 = 14       7 x 4 = 28       7 x 6 = 42       7 x 3 = 21

2 x 7 = 14       4 x 7 = 28       6 x 7 = 42       3 x 7 = 21

14 : 7 = 2       28 : 7 = 4       42 : 7 = 6       21 : 7 = 3

14 : 2 = 7       28 : 4 = 7       42 : 6 = 7       21 : 3 = 7

7 x 3 = 21    7 x 6 = 42    7 x 5 = 35    7 x 4 = 28

21 : 7 = 3    42 : 7 = 6    35 : 7 = 5    28 : 7 = 4

21 : 3 = 7    42 : 6 = 7    35 : 5 = 7    28 : 4 = 7

7 × 3 = 21      7 × 6 = 42   7 × 5 = 35.     7 × 4 = 28

21 : 7 = 3.     42 : 7 = 6.   35 : 7 = 5.     28 : 7 = 4

21 : 3 = 7.    42 : 6 = 7.   35 : 5 = 7.    28 : 4 = 7

A

A

A

\(\dfrac{26}{81}+\dfrac{4}{27}=\dfrac{26+12}{81}=\dfrac{38}{81}\)

\(\dfrac{5}{64}+\dfrac{7}{8}=\dfrac{5+56}{64}=\dfrac{61}{64}\)

\(\dfrac{26}{81}+\dfrac{4}{27}=\dfrac{26}{81}+\dfrac{4\times3}{27\times3}=\dfrac{26}{81}+\dfrac{12}{81}=\dfrac{38}{81}\)

\(\dfrac{5}{64}+\dfrac{7}{8}=\dfrac{5}{64}+\dfrac{7\times8}{8\times8}=\dfrac{5}{64}+\dfrac{56}{64}=\dfrac{61}{64}\)

a)

104 x 7 = 7 x 104

b)

9 x 30 = (20+10) x 9

c)

(6 x 15) x 21 = 6 x (15 x 21)

d)

23 x 3 x 4 = 4 x 69= 12 x 23

a: =>3/8x6/3<x<20/21x21/4

=>3/4<x<5

hay \(x\in\left\{1;2;3;4\right\}\)

b: =>56/42<x<11/2

=>4/3<x<11/2

nên \(x\in\left\{2;3;4;5\right\}\)

a: =>3/8x6/3<x<20/21x21/4

=>3/4<x<5

hay \(x\in\left\{1;2;3;4\right\}\)

b: =>56/42<x<11/2

=>4/3<x<11/2

nên \(x\in\left\{2;3;4;5\right\}\)

a, \(x=-\frac{21}{20}-\frac{-7}{15}\)

\(x=\frac{-7}{12}\)

b, \(\frac{7}{2}-x=\frac{-21}{20}:\frac{5}{4}\)

\(\frac{7}{2}-x=\frac{-21}{25}\)

\(x=\frac{7}{2}-\frac{-21}{25}\)

\(x=\frac{217}{50}\)

a)x=(-7/12)

b)x=(217/50)