a)

b)

3 x 4 + 8 = 12 + 8 = 30

48 : 8 + 7 = 6 + 7 = 13

9 : 9 x 0 = 1 x 0 = 0

7 x 10 – 14 = 70 – 14 = 56

72 : 9 – 6 = 8 – 6 = 2

0 : 6 + 37 = 0 + 37 = 37

8 x 2 = 16       8 x 3 = 24       8 x 4 = 32       8 x 5 = 40

16 : 8 = 2       24 : 8 = 3       32 : 8 = 4       40 : 8 = 5

8 x 6 = 48       8 x 7 = 56       8 x 8 = 64       8 x 9 = 72

48 : 8 = 6       56 : 8 = 7       64 : 8 = 8       72 : 8 = 9

16                         24                       32                 40

2                           3                        4                      5

48                         56                       64                   72

6                           7                         8                     9

Bài 4:

a: =>7/x-5=2

=>x-5=7/2

=>x=17/2

b: =>1-2x=-5

=>2x=6

=>x=3

c: =>2x-3=5 hoặc 2x-3=-5

=>2x=8 hoặc 2x=-2

=>x=-1 hoặc x=4

d: =>2(x+1)^2+17=21

=>2(x+1)^2=4

=>(x+1)^2=2

=>\(x+1=\pm\sqrt{2}\)

=>\(x=\pm\sqrt{2}-1\)

a, Ta có :

1996 + 3992 + 5988 + 7984

= 1 x 1996 + 2 x 1996 + 3 x 1996 + 4 x 1996

= (1 + 2 + 3 + 4) x 1996

= 10 x 1996

= 19960

b, 2 x 3 x 4 x 8 x 50 x 25 x 125

= 3 x 2 x 4 x 50 x 8 x 25 x 125

= 3 x (2 x 50) x (4 x 25) x (8 x 125)

= 30 000 000.

c, Ta nhận thấy :

45 x 128 – 90 x 64 = 45 x (2 x 64) – 90 x 64

= (45 x 2) x 64 – 90 x 64

= 90 x 64 – 90 = 0

Trong 1 tích có 1 thừa số bằng 0. Vậy tích đó bằng 0, tức là :

(45 x 46 + 47 x 48) x (51 x 52 – 49 x 48) x (45 x 128 – 90 x 64) x (1995 x 1996 + 1997 x 1998) = 0

a) \(\frac{x+1}{9}+\frac{x+2}{8}=\frac{x+3}{7}+\frac{x+4}{6}\)

\(\Rightarrow\left(\frac{x+1}{9}+1\right)+\left(\frac{x+2}{8}+2\right)=\left(\frac{x+3}{7}+1\right)+\left(\frac{x+4}{6}+1\right)\)

\(\Rightarrow\frac{x+10}{9}+\frac{x+10}{8}-\frac{x+10}{7}-\frac{x+10}{6}=0\)

\(\Rightarrow\left(x+10\right)\left(\frac{1}{9}+\frac{1}{8}-\frac{1}{7}-\frac{1}{6}\right)=0\)

Mà \(\frac{1}{9}+\frac{1}{8}-\frac{1}{7}-\frac{1}{6}\ne0\)

\(\Rightarrow x+10=0\)

\(\Rightarrow x=-10\)

Vậy x = -10

b) \(\frac{x+43}{57}+\frac{x+46}{54}=\frac{x+49}{51}+\frac{x+52}{48}\)

\(\Rightarrow\left(\frac{x+43}{57}+1\right)+\left(\frac{x+46}{54}+1\right)=\left(\frac{x+49}{51}+1\right)+\left(\frac{x+52}{48}+1\right)\)

\(\Rightarrow\frac{x+100}{57}+\frac{x+100}{54}=\frac{x+100}{51}+\frac{x+100}{48}\)

\(\Rightarrow\frac{x+100}{57}+\frac{x+100}{54}-\frac{x+100}{51}-\frac{x+100}{48}=0\)

\(\Rightarrow\left(x+100\right)\left(\frac{1}{57}+\frac{1}{54}-\frac{1}{51}-\frac{1}{48}\right)=0\)

Mà \(\frac{1}{57}+\frac{1}{54}-\frac{1}{51}-\frac{1}{48}\ne0\)

\(\Rightarrow x+100=0\)

\(\Rightarrow x=-100\)

Vậy x = -100

a.\(\frac{x+1}{9}+\frac{x+2}{8}=\frac{x+3}{7}+\frac{x+4}{6}\)

=>\(\frac{x+1}{9}+1+\frac{x+2}{8}+1=\frac{x+3}{7}+1+\frac{x+4}{6}+1\)

<=> \(\frac{x+1+9}{9}+\frac{x+2+8}{8}=\frac{x+3+7}{7}+\frac{x+4+6}{6}\)

<=>\(\frac{x+10}{9}+\frac{x+10}{8}=\frac{x+10}{7}+\frac{x+10}{6}\)

<=> \(\frac{x+10}{9}+\frac{x+10}{8}-\frac{x+10}{7}-\frac{x+10}{6}=0\)

<=> \(\left(x+10\right)\left(\frac{1}{9}+\frac{1}{8}-\frac{1}{7}-\frac{1}{6}\right)=0\)

<=> x+10=0

<=> x=-10

Vậy tập nghiệm của phương trình trên là S=\(\left\{-10\right\}\)

b. \(\frac{x+43}{57}+\frac{x+46}{54}=\frac{x+49}{51}+\frac{x+52}{48}\)

=> \(\frac{x+43}{57}+1+\frac{x+46}{54}+1=\frac{x+49}{51}+1+\frac{x+52}{48}+1\)<=>\(\frac{x+43+57}{57}+\frac{x+46+54}{54}=\frac{x+49+51}{51}+\frac{x+52+48}{48}\)​

<=>\(\frac{x+100}{57}+\frac{x+100}{54}=\frac{x+100}{51}+\frac{x+100}{48}\)

<=>\(\frac{x+100}{57}+\frac{x+100}{54}-\frac{x+100}{51}-\frac{x+100}{48}=0\)

<=>(x+100)\(\left(\frac{1}{57}+\frac{1}{54}-\frac{1}{51}-\frac{1}{48}\right)\)=0

<=>x+100=0

<=>x= -100

Vậy tập nghiệm của phương trình trên là S=\(\left\{-100\right\}\)

9*8*48+7*4*48+72*52+2*52*14

=72*48+28*48+72*52+28*52

=72 * ( 48 + 52 ) + 28 * ( 48 + 52 )

=72 * 100 + 28 * 100

=100 * ( 72 + 28 )

= 100 * 100

=10000

9 x 8 x 48 + 7 x 4 x 48 + 72 x 52 + 2 x 52 x 14 

= 72 x 48 + 28 x 48 + 72 x 52 + 2 x 14 x 52

= ( 72 + 28 ) x 48 + 72 x 52 + 28 x 52

= ( 72 + 28 ) x 48 + ( 72 + 28 ) x 52

=  100 x 48 + 100 x 52

= 100 x ( 48 + 52 )

= 100 x 100

= 10000

9 . 8 . 48 + 7 . 4 . 48 + 72 . 52 + 2 . 52 . 14

= 72 . 48 + 28 . 48 + 72 . 52 + 52 . 28

= 48 . ( 72 + 28 ) + 52 . ( 72 + 28 )

= 48 . 100 + 52 .100

= 100 . ( 48 + 52 )

= 100 . 100

= 10000

8 x 6 = 48

8 x7 = 56

8 x 8 = 64

8 x 9 = 72

48 : 8 = 6

56 : 8 = 7

64 : 8 = 8

72 : 8 = 9

a) \(\left(145\times99+145\right)-\left(143\times102-143\right)\)

\(=\left[145\times\left(99+1\right)\right]-\left[143\times\left(102-1\right)\right]\)

\(=\left(145\times100\right)-\left(143\times101\right)\)

\(=14500-14443\)

\(=57\)

b) \(54\times47-47\times53-20-27\)

\(=47\times\left(54-53\right)-20-27\)

\(=47-20-27\)

\(=0\)

c) \(10000-47\times72-47\times28\)

\(=10000-47\times\left(72+28\right)\)

\(=10000-47\times100\)

\(=10000-4700\)

\(=5300\)

d) \(3457-27\times48-48\times73+6543\)

\(=\left(3457+6543\right)-48\times\left(27+73\right)\)

\(=10000-48\times100\)

\(=10000-4800\)

\(=5200\)