9/13 x 7/12 + 9/13 x 5/12 - 9/13

= 9/13 x (7/12 + 5/12 - 1)

= 9/13 x 0

= 0

4/13 x 5/12 + 4/13 x 7/12 - 4/3

= 4/13 x (5/12 + 7/12) - 4/3

= 4/13 x 1 - 4/3

= 4/13 - 4/3

= -40/39

a) 9/13 x 7/12 + 9/13 x 5/12 - 9/13

= 9/13 x ( 5/12 + 7/12 - 1 )

= 9/13 x 0

= 0

b) 4/13 x 5/12 + 4/13 x 7/ 12 - 4/3

= 4/13 x ( 5/12 + 7/12 - 13/3 )

= 4/13 x ( - 10/3 )

= -40/39 

a, =>-2x+12+6x-60=8

=>4x+48=8

=>4x=56

=>x=14

b,=>-8x-36-8x-3-x-13=0

=>-17x-52=0

=>-17x=52

=>x=-52/17

c,=>14x+7x^2-7x^2-21x=14

=>-7x=14

=>x=-2

a <=> -2x+12 +6x-60-8=0

<=>4x-56=0

<=>x=56/4=14

Vậy S=(4)

a) \(y-6:2-\left(48-24.2:6-3\right)=0.\)

\(\Rightarrow y-3-\left(48-8-3\right)=0\)

\(\Rightarrow y-3-37=0\)

\(\Rightarrow y=0+37+3=40\)

Vậy y = 40

b) \(\left(7.13+8.13\right):\left(9\frac{2}{3}-y\right)=39\)

\(\Rightarrow195:\left(\frac{29}{3}-y\right)=39\)

\(\Rightarrow\frac{29}{3}-y=195:39=5\)

\(\Rightarrow y=\frac{29}{3}-5=\frac{14}{3}\)

Vậy y=\(\frac{14}{3}\)

a) y - 6 : 2 - ( 48 - 24 x 2 : 6 - 3 ) = 0

y - 6 : 2 - ( 48 - 48 : 6 - 3 ) = 0

y - 6 : 2 - ( 48 - 8 - 3 ) = 0

y - 6 : 2 - 37 = 0

y - 3 = 0 + 37

y - 3 = 37

y = 37 + 3

y = 40

b) ( 7 x 13 + 8 x 13 ) : (  \(9\frac{2}{3}\) - y ) = 39

( 15 x 13 ) : ( \(9\frac{2}{3}\) - y ) = 39

195 : ( \(9\frac{2}{3}\) - y ) = 39

\(9\frac{2}{3}\) - y = 195 : 39

\(9\frac{2}{3}-y=5\)

\(y=9\frac{2}{3}-5\)

\(y=\frac{14}{3}\)

`(x+19)/3 +(x+13)/5 = (x+7)/7 + (x+1)/9`

`<=> x/3 + 19/3 +x/5 +13/5 = x/7 +1 +x/9 +1/9`

`<=> x/3 +x/5 -x/7 -x/9 = 1+1/9 -19/3 -13/5`

`<=> x (1/3 +1/5 -1/7 -1/9) = -118/45`

`<=> x * 88/315 = -352/45`

`<=> x = -28`

Vậy `S={-28}`

ủa kì vậy cô tôi dạy kiểu như làm kiếm mẫu số chung gì mà...

Coi lại bài coi đúng không;-;; hoang mang quá đi ạ

a: =-5/9-4/9+8/15+7/15-2/11=-2/11

b: =10/17+7/17-5/13-8/13+11/25

=11/25

c: =(9/12-2/12)*3/2=7/12*3/2=21/24=7/8

d: =(31/10-25/10)*3-2

=3/5*3-2

=9/5-2

=-1/5

???????

sao toàn là bài khó vậy trời!

(13x7+13x8):(29/3-y)=39

=>[13x(7+8)]:(29/3-y)=39

=>(13x15):(29/3-y)=39

=>195:(29/3-y)=39

=>29/3-y=195:39=5

=>y=29/3-5

=>y=29/3-15/3

=>y=13/3

(13 x 7 + 13 x 8) : (29/3 - y) = 39

=> [13 x (7 + 8)] : (29/3 - y) = 39

=> (13 x 15) : (29/3 - y) = 39

=>195 : (29/3 - y) = 39

=> 29/3 - y = 195 : 39 = 5

=> y = 29/3 - 5

=> y = 29/3 - 15/3

=> y = 13/3

a. Tính đúng y = 40

b. Tính đúng  y = 4 2 3

x = 5/6 - 5/7

x = 5/42

x = 2/3 - 13/21

x = 1/21

\(x=\dfrac{5}{6}-\dfrac{5}{7}=\dfrac{5}{42}\)

\(x=\dfrac{2}{3}-\dfrac{13}{21}=\dfrac{1}{21}\)