a/ \(\frac{x-1}{9}=\frac{8}{3}\) 

\(\Leftrightarrow3\left(x-1\right)=72\)

\(\Leftrightarrow x-1=24\)

\(\Leftrightarrow x=25\)

Vậy ..

b/ \(\frac{-x}{4}=\frac{-9}{x}\)

\(\Leftrightarrow x^2=36\)

\(\Leftrightarrow x^2=6^2=\left(-6\right)^2\)

\(\Leftrightarrow\orbr{\begin{cases}x=6\\x=-6\end{cases}}\)

Vậy ..

c/ \(\frac{x}{4}=\frac{18}{x+1}\)

\(\Leftrightarrow x\left(x+1\right)=72\)

\(\Leftrightarrow x\left(x+1\right)=8.9\)

\(\Leftrightarrow x=8\)

Vậy ..

giup j zay bn

thiếu đề bạn ah

bạn ơi thiếu đề

a, \(\frac{x-1}{9}=\frac{8}{3}\)

\(\Rightarrow\left(x-1\right).3=8.9\)

\(\Rightarrow\left(x-1\right).3=72\)

\(\Rightarrow x-1=72:3\)

\(\Rightarrow x-1=24\)

\(\Rightarrow x=24+1\)

\(\Rightarrow x=25\)

b, \(\frac{-x}{4}=\frac{-9}{x}\)

\(\Rightarrow-x.x=-9.4\)

\(\Rightarrow-\left(x^2\right)=-36\)

\(\Rightarrow x^2=36\)

\(\Rightarrow\orbr{\begin{cases}x=6\\x=-6\end{cases}}\)

c, \(\frac{x}{4}=\frac{18}{x+1}\)

\(\Rightarrow x\left(x+1\right)=4.18\)

\(\Rightarrow x.x+x.1=72\)

\(\Rightarrow x^2+x=72\)

\(\Rightarrow x^2+x-72=0\)

\(\Rightarrow x^2+x-8^2+8=0\)

\(\Rightarrow x=8\)

a) x-1=24

=>x=24+1=25

=> x=25

b)=>-(x^2)=-36

=>x=6

k mik nha

a) \(\frac{x-1}{9}=\frac{8}{3}\)

\(\Leftrightarrow3\left(x-1\right)=9\cdot8\)

\(\Leftrightarrow3x-3=72\)

\(\Leftrightarrow3x=75\)

\(\Leftrightarrow x=25\)

a)\(\frac{x-1}{9}=\frac{8}{3}\)

(x-1)3=8.9

3x-3=72

3x=72+3

3x=75

x=75:3

x=25

b)\(\frac{-x}{4}=\frac{-9}{x}\)

(\(\frac{-x}{4}=\frac{-9}{x}\))=(\(\frac{x}{4}=\frac{9}{x}\))

x.x=9.4

^{x^2=36}

^{x^2=6^2}

^➤x=6

^{c)\(\frac{x}{4}=\frac{18}{x+1}\)}

^x(x+1)=18.4

^x(x+1)=72

^{(Ta có x và x+1 là hai số tự nhiên liên tiếp và một chẵn và một số lẻ)}

Ta có:Ư(72)=1;2;3;4;6;8;9;72;36;12;18;24

Và vì x và x+1 là 2 số tự nhiên liên tiếp, nên:

Ta có bảng sau

d)\(\frac{5}{12}=\frac{-x}{72}\)

(-x).12=5.72

(-x).12=360

(-x)=360:12

(-x)=30

➤x=-30

e)\(\frac{x+3}{-15}=\frac{1}{3}\)

(x+3)3=1.(-15)

3x+9=-15

3x=(-15)-9

3x=-24

x=(-24):3

➤x=-8

 mik ko chép lại đề, mik làm luôn: 

a)  x - \(\frac{31}{36}=\frac{-13}{38}\)

x = \(\frac{-13}{18}+\frac{31}{36}\)

\(x=\frac{5}{36}\)

b)\(2-x-\frac{3}{7}=\frac{9}{-21}\)

\(\frac{11}{7}-x=\frac{3}{7}\)

x = \(\frac{11}{7}-\frac{3}{7}\)

x = 8/7

c) x + 3/11 = 23/44

x = 23/44 - 3/11

x = 1/4

d) \(\frac{1}{12}-x=\frac{-11}{9}\)

x = \(\frac{1}{12}+\frac{11}{9}\)

x = 47/36

e) \(x-\frac{2}{3}=\frac{-17}{3}\)

x= -17/3 + 2/3

x = -5 

f) \(x-\frac{1}{2}=\frac{11}{4}.\frac{3}{11}\)

x - 1/2 = 3/4

x = 3/4 + 1/2 

x = 5/4

g) \(2x+\frac{3}{8}=\frac{-21}{32}.\frac{4}{7}\)

2x + 3/8 = -3 / 8

2x = -3/8 - 3/8 

2x = -9/8

x = -9/8.1/2 

x = -9/16

h) x - \(\frac{x}{3}=\frac{3}{57}.\frac{19}{12}\)

x  - \(\frac{x}{3}=\frac{1}{12}\)

x = \(\frac{1}{12}+\frac{x}{3}\)

x = \(\frac{1+4x}{12}\)

=> 12x = 1+4x

12x - 4x = 1

8x = 1

x = 1/8 

Trả lời nhanh gọn lẹ nhé, mình k cho :)

a) \(x-\frac{5}{12}-\frac{4}{9}=\frac{-13}{18}\)

  \(x-\frac{5}{12}=\frac{-13}{18}+\frac{4}{9}\)

  \(x-\frac{5}{12}=\frac{-13}{18}+\frac{8}{18}\)

  \(x-\frac{5}{12}=\frac{-5}{18}\)

 \(x=\frac{-5}{18}+\frac{5}{12}\)

....

a Đ

b S

c S

d Đ

a ) S 

b ) Đ

c ) S

d ) Đ

k cho mk nhé 

Mai Hồng Ngọc? Vũ Thị Thu Hằng? Ai đúng dzậy -_-*

e) \(\frac{-84}{14}< 3x< \frac{108}{9}\)

\(\Rightarrow-2< x< 4\)

Vậy \(-2< x< 4\)

d)  \(\frac{x-3}{y-3}=\frac{4}{3}\)

Ta có: x=y+5

\(\Rightarrow\frac{y+5-3}{y-3}=\frac{4}{3}\)

\(\Rightarrow\frac{y+2}{y-3}=\frac{4}{3}\)

\(\Rightarrow\left(y+2\right).3=\left(y-3\right).4\)

\(3y+6=4y-12\)

\(6+12=4y-3y\)

\(y=18\)

\(\Rightarrow x=5+y=5+18=23\)

KL:............................

a) \(\frac{x-1}{9}=\frac{8}{3}\)

\(\Rightarrow\)\(\left(x-1\right).3=9.8\)

\(3x-3=72\)

\(3x=75\)

\(x=\frac{75}{3}\)

\(x=25\)

Câu b tương tự

\(\frac{x}{4}=\frac{18}{x+1}\)

\(\Rightarrow x.\left(x+1\right)=4.18\)

\(x.\left(x+1\right)=72\)

\(x.\left(x+1\right)=8.9\)

\(\Rightarrow x=8\)

a) \(\frac{x-1}{9}=\frac{8}{3}\)

=>\(\frac{x-1}{9}=\frac{24}{9}\)

=> x-1=24

=> x = 25

b) -x/4 = -9/x

=> -x.x = -9.4

=> x^2 = 36

=> x = 6 hoặc x= -6

c) x/4 = 18/x+1

=> x(x+1)=18.4

=> x(x+1)=72=1.72=2.36=3.24=4.18=6.12=8.9

Vì x va x+1 là 2 số liên tiếp và x<x+1

nên x=8 và x+1 = 9

=> X = 8

#)Giải :

a) x + 2x + 3x + ... + 100x = - 213

=> 100x + ( 2 + 3 + 4 + ... + 100 ) = - 213 

=> 100x + 5049 = - 213 

<=> 100x = - 5262

<=> x = - 52,62

#)Giải :

b) \(\frac{1}{2}x-\frac{1}{3}=\frac{1}{4}x-\frac{1}{6}\)

\(\Rightarrow\frac{1}{2}x+\frac{1}{4}x=\frac{1}{3}+\frac{1}{6}\)

\(\Rightarrow\frac{1}{2}x+\frac{1}{4}x=\frac{1}{2}\)

\(\Rightarrow\left(\frac{1}{2}+\frac{1}{4}\right)x=\frac{1}{2}\)

\(\Rightarrow\frac{3}{4}x=\frac{1}{2}\)

\(\Leftrightarrow x=\frac{2}{3}\)

a) x + 2x + 3x + ... +100x = -213

=>  x . (1 + 2 + 3 +... + 100) = - 213

=> x . 5050 = -213

=> x           = - 213 : 5050

=> x           = -213/5050

b) \(\frac{1}{2}x-\frac{1}{3}=\frac{1}{4}x-\frac{1}{6}\)

=> \(\frac{1}{2}x-\frac{1}{4}x=\frac{1}{3}-\frac{1}{6}\)

=> \(x.\left(\frac{1}{2}-\frac{1}{4}\right)=\frac{1}{6}\)

=> \(x.\frac{1}{4}=\frac{1}{6}\)

=> \(x=\frac{1}{6}:\frac{1}{4}\)

=> \(x=\frac{2}{3}\)

c) 3(x-2) + 2(x-1) = 10

=> 3x - 6 + 2x - 2 = 10

=> 3x + 2x - 6 - 2 = 10

=> 5x - 8 = 10

=> 5x = 10 + 8

=> 5x = 18

=> x = 18:5

=> x = 3,6

d) \(\frac{x+1}{3}=\frac{x-2}{4}\)

=> \(4\left(x+1\right)=3\left(x-2\right)\)

=>\(4x+4=3x-6\)

=> \(4x-3x=-4-6\)

=> \(x=-10\)

a) x = 99/20

b) x = 7

c) x = 2

( chỉ lm đc đến đó thui nk )