Vì 18 chia hết cho x;24 chia hết cho x

=>x thuộc ƯC(18;24)

Ta có: 18=2.3^2     24=2^3.3

ƯC(18;24)=2.3=6

=>x=6

Bài 1: 

1: =-5/24+16/27+3/4

=-5/24+18/24+16/27

=13/24+16/27

=117/216+128/216=245/216

2: =-1/3+1/3+6/7=6/7

3: \(=\dfrac{1}{2}-\dfrac{7}{12}+\dfrac{1}{2}=1-\dfrac{7}{12}=\dfrac{5}{12}\)

4: \(=-\dfrac{5}{8}+\dfrac{14}{25}-\dfrac{6}{10}=\dfrac{-125+112-120}{200}=\dfrac{-133}{200}\)

1a) \(\frac{x-3}{x+7}=\frac{-5}{-6}\)

=> \(\frac{x-3}{x+7}=\frac{5}{6}\)

=> (x - 3).6 = 5.(x + 7)

=> 6x - 18 = 5x + 35

=> 6x - 5x = 35 + 18

=> x = 53

b) \(\frac{x-7}{x+3}=\frac{4}{3}\)

=> (x - 7). 3 = (x + 3). 4

=> 3x - 21 = 4x + 12

=> 3x - 4x = 12 + 21

=> -x = 33

=> x = -33

c) \(\frac{x-10}{6}=-\frac{5}{18}\)

=> (x - 10) . 18 = -5 . 6

=> 18x - 180 = -30

=> 18x = -30 + 180

=> 18x = 150

=> x = 150 : 18 = 25/3

d) \(\frac{x-2}{4}=\frac{25}{x-2}\)

=> (x - 2)(x - 2) = 25 . 4

=> (x - 2)² = 100

=> (x - 2)² = 10²

=> \(\orbr{\begin{cases}x-2=10\\x-2=-10\end{cases}}\)

=> \(\orbr{\begin{cases}x=12\\x=-8\end{cases}}\)

e) \(\frac{7}{x}=\frac{x}{28}\)

=> 7 . 28 = x . x

=> 196 = x²

=> x² = 14²

=> \(\orbr{\begin{cases}x=14\\x=-14\end{cases}}\)

f) \(\frac{40+x}{77-x}=\frac{6}{7}\)

=> (40 + x) . 7 = (77 - x).6

=> 280 + 7x = 462 - 6x

=> 280 - 462 = -6x + 7x

=> -182 = x

=> x = -182

36367 l'290209 92021

a ) x - ( - 18 ) = -24

x + 18 = -24

x = -24 - 18

x = -6

b ) -x - 17 + 8 = 33 - 19

-x - 17 + 8 = 14

-x - 17 = 14 - 8

-x - 17 = 6

-x =  -( 6 + 17 )

-x = - 23

c ) 15 - ( -4 + 7 ) = x - 14

15 + 4 + 7 = x - 14

27 = x - 14 

x - 14 = 27

x = 27 + 14

x = 41

d ) 9 - 25 = ( 7 - x ) - ( 25 + 7 ) 

( 7 - x ) - 32 = -16

7 - x = -16 + 32 

-7 - x = -16

x = -7 - ( - 16)

x = -7 + 16

x = 9

\((x-6)(3x-9)>0\)
TH1:
\(\orbr{\begin{cases}x-6< 0\\3x-9< 0\end{cases}}\)\(\Rightarrow\orbr{\begin{cases}x< 6\\x< 3\end{cases}}\)\(\Rightarrow x< 3\)
TH2:
\(\orbr{\begin{cases}x-6>0\\3x-9>0\end{cases}}\)\(\Rightarrow\orbr{\begin{cases}x>6\\x>3\end{cases}}\)\(\Rightarrow x>6\)
Vậy \(x< 3\) hoặc \(x>6\)thì \((x-6)(3x-9)>0\)
Học tốt!

20.
\((2x-1)(6-x)>0\)
TH1:
\(\orbr{\begin{cases}2x-1>0\\6-x>0\end{cases}\Rightarrow\orbr{\begin{cases}x< \frac{1}{2}\\x< 6\end{cases}}\Rightarrow x< 6}\)
TH2
\(\orbr{\begin{cases}2x-1< 0\\6-x< 0\end{cases}\Rightarrow\orbr{\begin{cases}x>\frac{1}{2}\\x>6\end{cases}}\Rightarrow x>\frac{1}{2}}\)
Vậy \(x< 6\)hoặc \(x>\frac{1}{2}\)thì \((2x-1)(6-x)>0\)
 

21.
\((2-x)(x+7)< 0\)
TH1.
\(\orbr{\begin{cases}2-x>0\\x+7< 0\end{cases}\Rightarrow\orbr{\begin{cases}x< 2\\x>-7\end{cases}}\Rightarrow-7< x< 2}\)
TH2.
\(\orbr{\begin{cases}2-x< 0\\x+7>0\end{cases}\Rightarrow\orbr{\begin{cases}x>2\\x< -7\end{cases}}\Rightarrow2< x< -7}\)(vô lí)
Vậy \(-7< x< 2\) thì \((2-x)(x+7)< 0\)
 

đi mà trả lời

=> 3x+7 = 5

<=> 3x = 5 - 7 = -2

<=> x = -2/3

(3x+7)² = 25

<=> 3x+7 = 25^-2

<=> 3x+7=5

<=> 3x=5-7

<=> 3x = -2

<=> x=\(\frac{-2}{3}\)

(3x + 7)² = 25 => 3x + 7 \(\in\left\{-5;5\right\}\)=> 3x \(\in\left\{-12;-2\right\}\)=> x = -4 (loại x = \(\frac{-2}{3}\)vì nó không thuộc Z)