<=> 7.( 12 - x ) = 9. ( 15 - x )

<=> 84 - 7x = 135 - 9x 

<=> 84 - 7x - ( 135 - 9x ) =0

<=> 84 - 7x - 135 + 9x = 0

<=> 2x - 51 = 0 

<=> 2x = 51 <=> x = 51/2 = 25,5

7/15 - x = 9/12 - x

So sánh 7/15 và 9/12

7/15 < 9/12 => ta có :

9/12 - 7/15 = 17/60 

=> Khi 7/15 trừ đi số nào thì 17/60 cộng thêm số đó

a) Ta có: \(x-12=\left(-9\right)-15\)

\(\Rightarrow x-12=-24\)

\(\Rightarrow x=-12\)

b) \(2-x=17-\left(-5\right)\)

\(\Rightarrow2-x=22\)

\(\Rightarrow x=2-22\)

\(\Rightarrow x=-20\)

c) \(11-\left(15+11\right)=x-\left(25-9\right)\)

\(\Rightarrow-15=x-16\)

\(\Rightarrow x=1\)

d) \(x-\left(17-x\right)=x-7\)

\(\Rightarrow x-17+x=x-7\)

\(\Rightarrow x+x-x=-7+17\)

\(\Rightarrow x=10\)

e) \(9-25=\left(7-x\right)-\left(25+7\right)\)

\(\Rightarrow9-25=7-x-25-7\)

\(\Rightarrow-16=-25-x\)

\(\Rightarrow x=-9\)

g) \(x-13=21-x\)

\(\Rightarrow x+x=21+13\)

\(\Rightarrow2x=34\)

\(\Rightarrow x=17\)

a, x - 12 = ( -9 ) - 15 

x - 12 = -24

x = -24 + 12

x = -12

b, 2 - x = 17 - ( -5 )

2 - x = 22

x = 2 - 22

x = -20

c, 11 - ( 15 + 11 ) = x - ( 25 - 9 )

11 - 26 = x - 16

-15 = x - 16

x = -15 + 16 

x = 1

d, x - ( 17 - x ) = x - 7

x - 17 + x = x - 7

x + x - 17 = x - 7

x + x - x = -7 + 17

x = 10

e.9 - 25 = ( 7- x ) - ( 25 + 7 )

-16 = ( 7 - x ) -32

7 - x = -32 + 16 

7 - x = 16

x = 7 - 16

x= -9

g, x - 13 = 21 - x

x + x = 21 + 13

2x = 44

x = 44 : 2

x=22

(2x - 1/3)= 2

2x= 2+1/3

2x= 7/3

x= 7/3 : 2

x= 1,66666

a: =>2x-1/3=2

=>2x=7/3

=>x=7/6

b: Sửa đề: 1/11-5/22

\(\dfrac{8}{9}:\left(\dfrac{1}{11}-\dfrac{5}{22}\right)+\dfrac{5}{9}:\left(\dfrac{1}{15}-\dfrac{2}{3}\right)\)

\(=\dfrac{8}{9}:\dfrac{-3}{22}+\dfrac{5}{9}:\dfrac{-9}{15}\)

\(=\dfrac{8}{9}\cdot\dfrac{-22}{3}+\dfrac{5}{9}\cdot\dfrac{-5}{3}\)

\(=\dfrac{-66-25}{27}=\dfrac{-91}{27}\)

=>3^x(1+3^2)=3^34+3^36

=>3^x.10=3^34.10

=>3^x=3^34

=>x=34

-15 ( x - 2 ) + 7 ( 3 - x ) = 7

-15x + 30 + 21 - 7x = 7

-15x - 7x = 7 - 21 - 30

-22x = -44

   x   = ( -44 ) : ( -22)

  x    = 2

Vậy x = 2

-12 ( x - 5 ) + 7 ( 3 - x ) = 5

-12x + 60 + 21 - 7x = 5

-12x - 7x = 5 - 21 - 60

-19x = -76

x      = ( -76 ) : (-19)

x      = 4

Vậy x = 4.

# HOK TỐT #

thanks

Giải:

X-12-15=20-7-18-X

X+X=20-7-18+12+15

2X=22

X=22:2

X=11

Phá ngoặc đẳng thức:

x-12-15=13-18-x

<=>x-27=-5-x

<=>x-27+5+x=0

<=>2x-22=0

<=>2x=22

<=>x=11

Vậy số nguyên x có giá trị là 11

a)72-3lx+1l=9

3lx+1l=63

x+1=+-21

th1 x=-21-1=-22

th2 x=21-1=20

b)43-lxl=-28

x=+-71

c)3lx-1l=12

x-1=+-4

th1 x=-4+1=-3

th2 x=4+1=5

-x + 20 = - (-15) - (8) + 13 

-x + 20 = 15 - 8 + 13 

-x + 20 = 7 + 13 

- x + 20 = 20

x = 20 - 20 

x = 0

-(-10) + x = -13 + (-9) + (-6) 

10 + x = -13 - 9 - 6 

10 + x = -28 

x = -28 - 10 

x = -38 

a) \(\frac{4}{5}=\frac{28}{35}\)

b) \(\frac{12}{15}=\frac{72}{90}\)

c) \(\frac{125}{300}=\frac{5}{12}\)

d) \(\frac{6}{9}=\frac{36}{54}\)

/HT\

a) \(\frac{4}{5}=\frac{28}{35}\)      \(\text{X}=28\)

b) \(\frac{12}{15}=\frac{72}{90}\)   \(\text{X}=90\)

c) \(\frac{125}{300}=\frac{5}{12}\)  \(\text{X}=12\)

d) \(\frac{6}{9}=\frac{36}{54}\)       \(\text{X}=6\)

=14/15*20/21*...*209/210

\(=\dfrac{4\cdot7}{5\cdot6}\cdot\dfrac{5\cdot8}{6\cdot7}\cdot...\cdot\dfrac{19\cdot22}{20\cdot21}\)

\(=\dfrac{4\cdot5\cdot6\cdot...\cdot19}{5\cdot6\cdot7\cdot...\cdot20}\cdot\dfrac{7\cdot8\cdot9\cdot...\cdot22}{6\cdot7\cdot8\cdot...\cdot21}=\dfrac{11}{15}\)