A = (2 + 2²) + (2³ + 2⁴ ) +…(2¹⁹⁹ + 2²⁰⁰)

A = 6 + 2² (2 + 2² ) +… + 2¹⁹⁸ (2 + 2²)

A = 6 + 2² (6 ) +… + 2¹⁹⁸ (6)

A = 6(1 + 2² +… + 2¹⁹⁸)

Vậy A chia hết cho 6

a) \(\left(\frac{2}{7}+\frac{3}{8}+\frac{12}{7}+\frac{5}{8}\right).\frac{19}{36}\)

\(=\left\{\left(\frac{2}{7}+\frac{12}{7}\right)+\left(\frac{3}{8}+\frac{5}{8}\right)\right\}.\frac{19}{36}\)

\(=\left(\frac{14}{7}+\frac{8}{8}\right).\frac{19}{36}\)

\(=\left(2+1\right).\frac{19}{36}\)

\(3.\frac{19}{36}=\frac{19}{12}\)

a)\(\dfrac{x}{60}=-\dfrac{3}{4}\)

\(\Rightarrow x\cdot4=60\cdot\left(-3\right)\)

   \(x\cdot4=-180\)

  x=45

b)\(\dfrac{2}{5}=\dfrac{12}{x}\)

   \(\Rightarrow2x=5\cdot12\)

      \(2x=60\)

       x=30

c)\(x-\dfrac{5}{7}=\dfrac{6}{21}\)

      \(x=\dfrac{2}{7}+\dfrac{5}{7}\)

      x=1

d)\(x+\dfrac{7}{8}=\dfrac{63}{24}\)

     \(x=\dfrac{21}{8}-\dfrac{7}{8}\)

     \(\dfrac{14}{8}\)

a)\(\dfrac{x}{60}=\dfrac{-3}{4}\Rightarrow x=\dfrac{-3.60}{4}=-45\)

b)\(\dfrac{2}{5}=\dfrac{12}{x}\Rightarrow x=\dfrac{5.12}{2}=30\)

a, \(\dfrac{38}{7}\) + ( \(\dfrac{16}{7}\) - \(\dfrac{5}{3}\))

= \(\dfrac{38}{7}\) + \(\dfrac{16}{7}\) - \(\dfrac{5}{3}\)

= \(\dfrac{54}{7}\) - \(\dfrac{5}{3}\)

= \(\dfrac{162}{21}\) - \(\dfrac{35}{21}\)

= \(\dfrac{127}{21}\)

b, \(\dfrac{29}{9}\) - ( \(\dfrac{14}{9}\) + \(\dfrac{11}{9}\) )

= \(\dfrac{29-14-11}{9}\)

= \(\dfrac{4}{9}\)

c, ( \(\dfrac{2}{7}\) + \(\dfrac{3}{8}\) + \(\dfrac{12}{7}\) + \(\dfrac{5}{8}\) ) - \(\dfrac{19}{63}\)

= ( \(\dfrac{2+12}{7}\) + \(\dfrac{3+5}{8}\)) - \(\dfrac{19}{63}\)

= \(\left(1+2\right)\) - \(\dfrac{19}{63}\)

= \(3-\dfrac{19}{63}\)

= \(\dfrac{189}{63}\) - \(\dfrac{19}{63}\)

= \(\dfrac{170}{63}\)

d, \(\dfrac{3}{7}\) . \(\dfrac{4}{9}\) + \(\dfrac{4}{9}\) . \(\dfrac{4}{7}\) - \(\dfrac{4}{9}\)

= \(\dfrac{4}{9}\) . ( \(\dfrac{3}{7}\) + \(\dfrac{3}{7}\) ) - \(\dfrac{4}{9}\)

= \(\dfrac{4}{9}\) . \(1-\dfrac{4}{9}\)

= \(\dfrac{4}{9}\) - \(\dfrac{4}{9}\)

= 0

chú ý dấu chấm là dấu nhân

`4/7+4`

`=4/7+4/1`

`=4/7+28/7`

`=32/7`

__

`3+6/11`

`=33/11+6/11`

`=39/11`

__

`3-5/7`

`=3/1-5/7`

`=21/7-5/7`

`=16/7`

__

`21/9-2`

`=21/9-18/9`

`=3/9`

`=1/3`

__

`15/24+2`

`=15/24+48/24`

`=63/24`

`=21/16`

__

`63/45-20/25`

`=63/45-4/5`

`=63/45-36/45`

`=27/45`

`=9/15`

__

`3/4-2/8`

`=3/4-1/4`

`=2/4`

__

`6/7-5/8`

`=48/56-35/56`

`=13/56`

__

`37/45-5/9`

`=37/45-25/45`

`=12/45`

`=4/15`

__

`46/39-11/13`

`=46/39-33/39`

`=13/39`

`=1/2`

__

`5/12+3/4+1/3`

`=5/12+9/12+4/12`

`=14/12+4/12`

`=18/12`

`=3/2`

__

`1/2+3/7+11/14`

`=7/14+6/14+11/14`

`=13/14+11/14`

`=24/14`

`=12/7`

__

`7/10-(1/5+1/4)`

`=7/10-(4/20+5/20)`

`=7/10-9/20`

`=14/20-9/20`

`=5/20`

`=1/4`

__

`15/4-2/3-3/4`

`=(15/4-3/4)-2/3`

`=12/4-2/3`

`=3-2/3`

`=9/3-2/3`

`=7/3`

6 x 4 = 24       12 : 6 = 2       7 x 3 = 21       63 : 7 = 9

7 x 5 = 35       42 : 7 = 6       6 x 8 = 48       48 : 6 = 8

6 x 6 = 36       28 : 7 = 4       7 x 8 = 56       49 : 7 = 7

6 x 4 = 24                    12 : 6 = 02                   7 x 3 = 21                 63 : 7 = 09                               7 x 5 = 35                       42 : 7 = 06

6 x 8 = 48                    48 :6 = 8                    6 x 6 = 36                 28 : 7 = 04                     7 x 8 = 56                            49 : 7 = 07

nbbbbbbbbbbbn 

a)\(12-\left[25+\left(6+3\right)^2\right]\)

\(=12-\left[25+9^2\right]\)

\(=12-\left[25+81\right]\)

\(=12-106\)

\(=\left(-94\right)\)

b) \(315-\left(8^6\div8^4-12.3+7+7^3\right)\)

\(=316-\left(8^2-36+7+343\right)\)

\(=316-\left(64-43+343\right)\)

\(=316-\left(21+343\right)\)

\(=316-364\)

\(=\left(-48\right)\)

c) \(-81-108\)

 \(=-\left(81+108\right)\)

\(=\left(-189\right)\)

d) \(-13-91\)

\(=-\left(13+91\right)\)

\(=\left(-104\right)\)

e)\(-85-\left(-17\right)\)

\(=-85+17\)

\(=-\left(85-17\right)\)

\(=\left(-68\right)\)

g) \(63.\left(-8\right)+\left(-63\right).92\)

\(=63.\left(-8\right)+63.\left(-92\right)\)

\(=63.\left[\left(-8\right)+\left(-92\right)\right]\)

\(=63.\left(-100\right)\)

\(=\left(-6300\right)\)

7 x 8 = 56       16 : 2 = 8       36 : 6 = 6       49 : 7 = 7

2 x 5 = 10       72 : 8 = 9       9 x 3 = 27       63 : 7 = 9

6 x 4 = 24       25 : 5 = 5       4 x 8 = 32       7 x 5 = 35

7 x 8 = 56

2 x 5 = 10

6 x 4 = 24

16 : 2 = 8 

72 : 8 = 9

25 : 5 = 5

36 : 6 = 6

9 x 3 = 27

4 x 8 = 32

49 : 7 = 7

63 : 7 = 9

7 x 5 = 35

9 x 5 = 45

63 : 7 = 9

8 x 8 = 64

5 x 7 = 35

8 x 7 =56

3 x 8 = 24

40 : 5 = 8

5 x 5 = 25

7 x 5 = 35

7 x 8 =56

6 x 4 = 24

45 : 9 = 5

7 x 7 = 49

35 : 5 = 7

56 : 8 = 7

2 x 8 = 16

81 : 9 = 9

9 x 9 = 81

35 : 7 = 5

56 : 7 = 8

ay bạn ơi dễ vậy mà

giúp mình với mọi người ơi, mình cần gấp :(