\(\dfrac{3x}{2\cdot5}+\dfrac{3x}{5\cdot8}+\dfrac{3x}{8\cdot11}+\dfrac{3x}{11\cdot14}=\dfrac{1}{21}\\ x\cdot\left(\dfrac{3}{2\cdot5}+\dfrac{3}{5\cdot8}+\dfrac{3}{8\cdot11}+\dfrac{3}{11\cdot14}\right)=\dfrac{1}{21}\\ x\cdot\left(\dfrac{1}{2}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{14}\right)=\dfrac{1}{21}\\ x\cdot\left(\dfrac{1}{2}-\dfrac{1}{14}\right)=\dfrac{1}{21}\\ x\cdot\dfrac{3}{7}=\dfrac{1}{21}\\ x=\dfrac{1}{21}:\dfrac{3}{7}\\ x=\dfrac{1}{9}\)

\(\frac{3x}{2\cdot5}+\frac{3x}{5\cdot8}+\frac{3x}{8\cdot11}+\frac{3x}{11\cdot14}=\frac{1}{21}\)

\(=>\frac{3x}{3}\left[\frac{3}{2\cdot5}+\frac{3}{5\cdot8}+\frac{3}{8\cdot11}+\frac{3}{11\cdot14}\right]=\frac{1}{21}\)

\(=>x\left[\frac{3}{2\cdot5}+\frac{3}{5\cdot8}+\frac{3}{8\cdot11}+\frac{3}{11\cdot14}\right]=\frac{1}{21}\)

\(=>x\left[\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+...+\frac{1}{11}-\frac{1}{14}\right]=\frac{1}{21}\)

\(=>x\left[\frac{1}{2}-\frac{1}{14}\right]=\frac{1}{21}\)

\(=>x\cdot\frac{3}{7}=\frac{1}{21}\Leftrightarrow x=\frac{1}{9}\)

\(\frac{3x}{2.5}+\frac{3x}{5.8}+\frac{3x}{8.11}+\frac{3x}{11.14}=\frac{1}{21}\)

=> \(x\left(\frac{3}{2.5}+\frac{3}{5.8}+\frac{3}{8.11}+\frac{3}{11.14}\right)=\frac{1}{21}\)

=> \(x\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}\right)=\frac{1}{21}\)

=> \(x\left(\frac{1}{2}-\frac{1}{14}\right)=\frac{1}{21}\)

=> \(x.\frac{3}{7}=21\)

=> x = 49 

Vậy x = 49

Xin lỗi bạn nhé x = 1/9 bước cuối mình ghi sót 

https://olm.vn/hoi-dap/tim-kiem?q=T%C3%ACm+x,+bi%E1%BA%BFt:+3x2.5++3x5.8++3x8.11++3x11.14+=121+&id=81551

Cậu vào link này nhé(đây là đáp án câu này)

Mấy bài này căng vậy?

a)4(18 - 5x) - 12(3x - 7) = 15(2x - 16) - 6(x + 14)

<=>72 - 20x - 36x +84 = 30x - 240 - 6x 84

<=> -80x = -480

<=> x = 6

b) 5(3x+5)-4(2x-3) =5x+3(2x+12)+1

<=> 15x + 25  - 8x + 12 = 5x + 6x + 36 + 1

<=> 15x + 25 - 8x + 12 - 5x - 6x - 36 - 1 = 0

<=> -4x = 0

<=> x = 0

c) 2(5x-8)-3(4x-5)=4(3x-4)+11

= 10x - 16 - 12x + 15 = 12x - 16 + 11

= -14x = -4

= x =\(\frac{2}{7}\)

d) 5x-3{4x-2[4x-3(5x-2)]}=182

= 5x - 3 . [4x - 2(4x - 15x + 6)]

= 5x - 3 . (4x - 8x + 30x - 12)

= 5x - 12x + 24x - 90x + 36

= -73x + 36 = 182

=> -73x = 182 - 36 = 146

=> x = 146 : (-73) = -2

~Hok tốt~

1. 3y = 0

=> y = 0

2. 1+x = 0

<+ x = -1

3.

\(1-2t=0\)

\(\Leftrightarrow2t=1\)

\(\Leftrightarrow\dfrac{1}{2}\)

4. 2x +x + 3 =0

\(\Leftrightarrow3x+3=0\)

\(\Leftrightarrow x=-3\)

5.

\(25x-20=0\)

\(\Leftrightarrow25x=20\)

\(\Leftrightarrow x=\dfrac{4}{5}\)

7.

2x-3 = x+5

<=> 2x - x = 5+3

<=> x = 8

8.

x-8=2x+3

<=> x - 2x = 3+8

<=> -x = 11

<=> x = -11

9. 17-2x = 3x-5

<=> -2x-3x = -5-17

<=> -5x = -22

<=> x = \(\dfrac{22}{5}\)

10.

2x+x+22=0

<=> 3x+22=0

<=> 3x = -22

<=> x = \(\dfrac{-22}{3}\)

Mấy bài kia tự giải tương tự nhá!!!

20) -5-(x + 3) = 2 - 5x ⇔ -5 - x - 3 = 2 -5x ⇔ 4x = 10 ⇔ x = \(\frac{5}{2}\)

Vậy...

Mấy cái này chuyển vế đổi dấu là xong í mà :3

1,

16-8x=0

=>16=8x

=>x=16/8=2

2, 

7x+14=0

=>7x=-14

=>x=-2

3,

5-2x=0

=>5=2x

=>x=5/2

Mk làm 3 cau làm mẫu thôi

Lúc đăng đừng đăng như v :>

chi ra khỏi ngt nản

từ câu 1 đến câu 8 cs thể làm rất dễ,bn tham khảo bài của bn muwaa r làm những câu cn lại