a: =>4x-5=0 hoặc 5/4x-2=0

=>x=5/4 hoặc x=2:5/4=2*4/5=8/5

b: =>(1/12+19/6-30,75)*x-8=102

=>-55/2x=110

=>x=-4

\(a,\dfrac{3}{4}x-\dfrac{2}{3}x=\dfrac{2}{7}\times\dfrac{1}{6}+\dfrac{5}{7}\times\dfrac{1}{6}\)

\(\dfrac{9}{12}x-\dfrac{8}{12}x=\dfrac{1}{6}\times\left(\dfrac{2}{7}+\dfrac{5}{7}\right)\)

\(\dfrac{1}{12}x=\dfrac{1}{6}\)

\(x=\dfrac{1}{6}:\dfrac{1}{12}\)

\(x=\dfrac{1}{6}\times12\)

\(x=2\)

9. (x + 28) = 0

x + 28 = 0: 9

x + 28 = 0

x = 0 – 28

x = -28

Vậy x = -28. 

720:[41-(2x-5)]=2³.5

720:[41-(2x-5)]=8.5

720:[41-(2x-5)]=40

41-(2x-5)=720:40

41-(2x-5)=18

2x-5=41-18

2x-5=23

2x=23+5

2x=28

x=28:2

x=14

Vậy x=14

 b) 720:[41 -(2x-5)]= 8 . 5

720:[41-(2x-5)]=40

[41-(2x-5)]=720 : 40

[41-(2x-5)]=18 

2x-5=41-18

2x-5=23

2x=23+5

2x=28

x=28:2

x=14

Vậy x=14

chắc vại ;-;

`a,(5-x)(x-1) < 0`

`<=>5-x<0` hoặc `x-1<0`

`<=>5 <x` hoặc `x<1`

Vậy `S={x|5<x;x<1}`

`b,(x-4)(x+1/2) >= 0`

`<=>TH1 : {(x-4>=0),(x+1/2 >=0):}<=>{(x>=4(TM)),(x>= -1/2(L)):}`

`<=>TH2 :{(x-4<=0),(x+1/2 <= 0):} <=>{(x<=4(L)),(x<=-1/2(TM)):}`

`=>x<= -1/2` hoặc `x>=4`

Vậy `S={x|x<= -1/2 ; x>=4}`

a) \(x^3+4x=0\)

\(\Rightarrow x\left(x^2+4\right)=0\)

\(\Rightarrow\left[\begin{array}{nghiempt}x=0\\x^2+4=0\end{array}\right.\)

\(\Rightarrow\left[\begin{array}{nghiempt}x=0\\x^2=-4\end{array}\right.\)

\(\Rightarrow\left[\begin{array}{nghiempt}x=0\\x\in\phi\end{array}\right.\)

Vậy: \(x=0\)

b) \(2\left(5-x\right)=4x-3\)

\(\Rightarrow10-2x=4x-3\)

\(\Rightarrow10+3=4x+2x\)

\(\Rightarrow13=6x\)

\(\Rightarrow x=\frac{13}{6}\)

x³+ 4x=0

<=> x(x²+4)=0

=> x=0 hoặc x²+4=0

Mà: x²+4 >4

=>x=0

a: x=5:(-1/2)=-10

b: x=8/3+1/9=25/9

c: =>x+5/6=11/21

=>x=-13/42

d: =>7/4x-5=-10/3

=>7/4x=5/3

=>x=20/21

e: =>10/3-3/4:x=-1/6

=>3/4:x=10/3+1/6=21/6=7/2

=>x=3/4:7/2=3/4*2/7=6/28=3/14

g: =>3/(x+5)=3/20

=>x+5=20

=>x=15

h: =>1-1/2+1/2-1/3+...+1/x-1/x+1=49/50

=>1-1/x+1=49/50

=>x+1=50

=>x=49

\(\left(4x-2\right)\left(x+5\right)=0\)

\(\Rightarrow\orbr{\begin{cases}4x-2=0\\x+5=0\end{cases}\Rightarrow\orbr{\begin{cases}x=\frac{1}{2}\\x=-5\end{cases}}}\)

\(\left(4x-2\right)\left(x+5\right)=0\)

\(\Rightarrow\orbr{\begin{cases}4x-2=0\\x+5=0\end{cases}}\Rightarrow\orbr{\begin{cases}4x=2\\x=-5\end{cases}}\Rightarrow\orbr{\begin{cases}x=\frac{1}{2}\\x=-5\end{cases}}\)

Vậy \(x\in\left\{-5;\frac{1}{2}\right\}\)

a: =>x:2,2=15,2x2=30,4

=>x=66,88

b: =>(15/4x+3/4)=-2/3

=>15/4x=-17/12

hay x=-17/45