39 + (31 - x) = 70

31 - x = 70 - 39

31 - x = 31

x = 31 - 31

x = 0

39 + ( 31 - x ) = 70

31 - x              = 70 - 39

31 - x              = 31

x                      = 31 - 31

x                      = 0 .

a) 39 + ( 31 - x ) = 70

31 - x = 39 + 70

31 - x = 109

=> x = 31 - 109

=> x = -78

39 + ( 31 - x ) = 70

         31 - x = 70 - 39

         31 - x = 31

               x = 31 - 31

               x = 0

TL

a)    5x + 20 = 110      

<=> x = 90 : 5 = 18

 b) x + 18 = - 13 

 <=> x = - 31

  c) 120 - x =  50   

   <=> x = 70     

 d) 10 - x = -29  

     <=>  x = 39

e) - x + 31 = 61

<=> x = -30

f) -85 - x = --70

<=> x = 15

Khi nào rảnh vào kênh H-EDITOR xem vid nha!!! Thanks!

Khiếp

2 . 53 . 27 + 6 . 9 . 87 - 3 . 18 . 40 
= 2. 53 . 9 . 3 + 2. 3 .9 .87 - 3 .2 .9 .40
= 54.53+54.87-54.40
=54(53+87-40)
=54. 100=5400

12 . 25 + 29 . 25 + 59 . 25 
= 25 . ( 12+29+59)
=25 . 90
=2250

43 . 37 + 93 . 43 + 57 . 61 + 69 . 57 
= 43.(37+93)+57(61+69)
=43.130+57.130
=130.(43+57)
=130.100
=13 000

12 . 53 + 53 . 172 - 53 
=53(12+172-1)
=53.184
=9752

35 . 54 + 35 . 58 + 65 . 75 + 65 . 45 
=35(54+58)+65(75+45)
=35.112+65.120
=3920+7800
=11720

39 . 8 + 70 . 3 + 31 . 8 
=8(39+31)+70.3
=8.70+70.3
=70.(8+3)
=70.11
=770

a) 39 + ( 31 - x ) = 70

31 - x = 70 - 39

31 - x = 31

x = 31 - 31

x = 0

b) K đủ dữ liệu

c) 7( x - 9 ) = 35

x - 9 = 35 : 7

x - 9 = 5

x = 5 + 9

x = 14

d) 42 - ( 2x + 32 ) + 12 : 2 = 6

42 - ( 2x + 32 ) + 6 = 6

42 - ( 2x + 32 ) = 6 - 6

42 - ( 2x + 32 ) = 0

2x + 32 = 42 - 0

2x + 32 = 42

2x = 42 - 32

2x = 10

x = 10 : 2

x = 5

`@` `\text {Ans}`

`\downarrow`

`280 \div (31-3x)=70`

`=> 31-3x = 280 \div 70`

`=> 31 - 3x = 4`

`=> 3x = 31 - 4`

`=> 3x = 27`

`=> x= 27 \div 3`

`=> x = 9` 

Vậy, `x=9.`

\(280:\left(31-3x\right)=70\)

\(=>31-3x=280:70\)

\(=>31-3x=4\)

\(=>3x=31-4\)

\(=>3x=27\)

\(=>x=27:3\)

\(=>x=9\)

Chúc bạn học tốt

\(\frac{3}{5.8}+\frac{11}{8.19}+\frac{12}{19.31}+\frac{70}{31.101}+\frac{99}{101.200}=\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{19}+\frac{1}{19}-\frac{1}{31}+\frac{1}{31}-\frac{1}{101}+\frac{1}{101}-\frac{1}{200}=\frac{1}{5}-\frac{1}{200}=\frac{39}{200}\)

=1/5-1/8+1/8-1/19+1/19-1/31+1/31-1/101+1/101-1/200=1/5-1/200=40/200-1/200=39/200

a) \(31\cdot72+\left(-31\right)\cdot70-2\cdot70\)

\(=31\cdot72-31\cdot70-2\cdot70\)

\(=31\cdot\left(72-70\right)-2\cdot70\)

\(=31\cdot2-2\cdot70\)

\(=2\cdot\left(31-70\right)\)

\(=2\cdot-39\)

\(=-78\) 

b) \(25\cdot\left(32+17\right)-32\cdot\left(25+47\right)\)

\(=25\cdot32+25\cdot17-32\cdot25-32\cdot47\) 

\(=25\cdot\left(32-32+17\right)-32\cdot47\)

\(=25\cdot17-32\cdot47\)

\(=425-1504\)

\(=-1079\)

Đề như thế nào vậy?

Nư thế này :\(D=\dfrac{3}{5.8}+\dfrac{11}{8.19}+\dfrac{12}{19.31}+\dfrac{70}{31.101}+\dfrac{99}{101.200}\)

Hay là \(D=\dfrac{3}{5}.8+\dfrac{11}{8}.19+\dfrac{12}{19}.31+\dfrac{70}{31}.101+\dfrac{99}{101}.200\)

Nếu là cách đầu thì mình làm thế này:

\(D=\dfrac{3}{5.8}+\dfrac{11}{8.19}+\dfrac{12}{19.31}+\dfrac{70}{31.101}+\dfrac{99}{101.200}\)

\(D=\dfrac{1}{5}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{19}+\dfrac{1}{19}-\dfrac{1}{31}+\dfrac{1}{31}-\dfrac{1}{101}+\dfrac{1}{101}-\dfrac{1}{200}\)

\(D=\dfrac{1}{5}-\dfrac{1}{200}\)

\(D=\dfrac{39}{200}\)

Vậy \(D=\dfrac{39}{200}\)

X x 3/5 + X x 2/7 = 31/70

=> X x (3/5+2/7) = 31/70

=> X x 31/35 = 31/70

=> X = 31/70 : 31/35

=> X = 31/70 x 35/31

=> X = 1/2

X x 3/5 + X x 2/7 = 31/70

X x [ 3/5 + 2/7 ] = 31/70

X x 31/35 = 31/70

X = 31/70 : 31/35

X= 1/2