\(\frac{3}{3.6.9}+\frac{3}{6.9.12}+\frac{3}{9.12.15}+\frac{3}{12.15.18}=\frac{3}{6}\left(\frac{6}{3.6.9}+\frac{6}{6.9.12}+\frac{6}{9.12.15}+\frac{6}{12.15.18}\right)\)

= \(\frac{1}{2}\left(\frac{1}{3.6}-\frac{1}{6.9}+\frac{1}{6.9}-\frac{1}{9.12}+\frac{1}{9.12}-\frac{1}{12.15}+\frac{1}{12.15}-\frac{1}{15.18}\right)\)

\(=\frac{1}{2}\left(\frac{1}{3.6}-\frac{1}{15.18}\right)=\frac{1}{2}.\frac{14}{270}=\frac{7}{270}\)

\(=\dfrac{12}{15}\times\left(\dfrac{26}{11}-\dfrac{9}{11}-\dfrac{6}{11}\right)=\dfrac{12}{15}\times\dfrac{11}{11}=\dfrac{12}{15}=\dfrac{4}{5}\)

= 12/15 x (26/11 - 9/11 - 6/11)

= 12/15 x 11/11

= 12/15

help

a: 3km75m=3,075m

\(\dfrac{1}{4}m^2=25dm^2\)

3h15'=195p

b: 26320:35=752

c: =3/5(5/12+7/12)

=3/5

a, \(3km75m=3075m\)

\(\dfrac{1}{4}m^2=25\text{d}m^2\)

`3` giờ `15` phút = `195` phút

b,

`->26320 : 35=752.`

c, \(\dfrac{9}{15}\times\dfrac{5}{12}+\dfrac{9}{15}\times\dfrac{7}{12}=\dfrac{9}{15}\times\left(\dfrac{5}{12}+\dfrac{7}{12}\right)=\dfrac{9}{15}\times1=\dfrac{9}{15}\)

`@mt`

Bạn ơi bạn làm đc bao nhiêu thì làm phụ mình nhé 

bài1

a, 

5 - 7 + 3 +(-8)

= -2 + 3 + ( - 8)

=     1    + (-8)= -7

a; - (-5) - (+7) + (+3) + (-8)

  = 5 - 7 + 3  - 8

= (5 + 3 - 8) - 7

= (8 - 8) - 7

= 0 - 7

= - 7

`5`

`a, -7/21 +(1+1/3)`

`=-7/21 + ( 3/3 + 1/3)`

`=-7/21+ 4/3`

`=-7/21+ 28/21`

`= 21/21`

`=1`

`b, 2/15 + ( 5/9 + (-6)/9)`

`= 2/15 + (-1/9)`

`= 1/45`

`c, (9-1/5+3/12) +(-3/4)`

`= ( 45/5-1/5 + 3/12)+(-3/4)`

`= ( 44/5 + 3/12)+(-3/4)`

`= 9,05 +(-0,75)`

`=8,3`

`6`

`x+7/8 =13/12`

`=>x= 13/12 -7/8`

`=>x=5/24`

`-------`

`-(-6)/12 -x=9/48`

`=> 6/12 -x=9/48`

`=>x= 6/12-9/48`

`=>x=5/16`

`---------`

`x+4/6 =5/25 -(-7)/15`

`=>x+4/6 =1/5 + 7/15`

`=> x+ 4/6=10/15`

`=>x=10/15 -4/6`

`=>x=0`

`----------`

`x+4/5 = 6/20 -(-7)/3`

`=>x+4/5 = 6/20 +7/3`

`=>x+4/5 = 79/30`

`=>x=79/30 -4/5`

`=>x= 79/30-24/30`

`=>x= 55/30`

`=>x= 11/6`

\(5)\)

\(A=\dfrac{-7}{21}+\left(1+\dfrac{1}{3}\right)\)

\(A=\dfrac{-7}{21}+\dfrac{4}{3}\)

\(A=\dfrac{-7}{21}+\dfrac{28}{21}\)

\(A=1\)

\(--------------\)

\(B=\dfrac{2}{15}+\left(\dfrac{5}{9}+\dfrac{-6}{9}\right)\)

\(B=\dfrac{2}{15}+\dfrac{-1}{9}\)

\(B=\dfrac{18}{135}+\dfrac{-15}{135}\)

\(B=\dfrac{1}{45}\)

\(------------\)

\(C=9-\dfrac{1}{5}+\dfrac{3}{12}+\dfrac{-3}{4}\)

\(C=\dfrac{44}{5}+\dfrac{3}{12}+\dfrac{-3}{4}\)

\(C=\dfrac{528}{60}+\dfrac{15}{60}+\dfrac{-3}{4}\)

\(C=\dfrac{181}{20}+\dfrac{-3}{4}\)

\(C=\dfrac{181}{20}+\dfrac{-15}{20}\)

\(C=\dfrac{83}{10}\)

\(6)\)

\(a)\) \(x+\dfrac{7}{8}=\dfrac{13}{12}\)

\(x=\dfrac{13}{12}-\dfrac{7}{8}\)

\(x=\dfrac{104}{96}-\dfrac{84}{96}\)

\(x=\dfrac{5}{24}\)

\(b)\) \(\dfrac{-6}{12}-x=\dfrac{9}{48}\)

\(\dfrac{-1}{2}-x=\dfrac{3}{16}\)

\(x=\dfrac{-1}{2}-\dfrac{3}{16}\)

\(x=\dfrac{-8}{16}-\dfrac{3}{16}\)

\(x=\dfrac{-11}{16}\)

\(c)\) \(x+\dfrac{4}{6}=\dfrac{5}{25}-\left(-\dfrac{7}{15}\right)\)

\(x+\dfrac{4}{6}=\dfrac{5}{25}+\dfrac{7}{15}\)

\(x+\dfrac{4}{6}=\dfrac{75}{375}+\dfrac{105}{375}\)

\(x+\dfrac{4}{6}=\dfrac{12}{25}\)

\(x=\dfrac{12}{25}-\dfrac{4}{6}\)

\(x=\dfrac{72}{150}-\dfrac{100}{150}\)

\(x=\dfrac{-14}{75}\)

\(d)\) \(x+\dfrac{4}{5}=\dfrac{6}{20}-\left(-\dfrac{7}{3}\right)\)

\(x+\dfrac{4}{5}=\dfrac{6}{20}+\dfrac{7}{3}\)

\(x+\dfrac{4}{5}=\dfrac{18}{60}+\dfrac{140}{60}\)

\(x+\dfrac{4}{5}=\dfrac{79}{30}\)

\(x=\dfrac{79}{30}-\dfrac{4}{5}\)

\(x=\dfrac{79}{30}-\dfrac{24}{30}\)

\(x=\dfrac{11}{6}\)

Giải:

\(A=\dfrac{-7}{21}+\left(1+\dfrac{1}{3}\right)\)

\(A=\dfrac{-7}{21}+\dfrac{4}{3}\)

\(A=\dfrac{-7}{21}+\dfrac{28}{21}\)

\(A=\dfrac{21}{21}=1\)

\(B=\dfrac{2}{15}+\left(\dfrac{5}{9}+\dfrac{-6}{9}\right)\)

\(B=\dfrac{2}{15}+\dfrac{-1}{9}\)

\(B=\dfrac{6}{45}+\dfrac{-5}{45}\)

\(B=\dfrac{1}{45}\)

\(C=\left(9-\dfrac{1}{5}+\dfrac{3}{12}\right)+\dfrac{-3}{4}\)

\(C=\left(\dfrac{44}{5}+\dfrac{1}{4}\right)+\dfrac{-3}{4}\)

\(C=\dfrac{181}{20}+\dfrac{-3}{4}\)

\(C=\dfrac{181}{20}+\dfrac{-15}{20}\)

\(C=\dfrac{166}{20}\)

Bài 6:

\(a)x+\dfrac{7}{8}=\dfrac{13}{12}\)

⇔\(x=\dfrac{13}{12}-\dfrac{7}{8}=\dfrac{5}{24}\)

\(b)\dfrac{-6}{12}-x=\dfrac{9}{48}\)

⇔\(x=\dfrac{-6}{12}-\dfrac{9}{48}=\dfrac{-11}{16}\)

\(c)x+\dfrac{4}{6}=\dfrac{5}{25}-\dfrac{-7}{15}\)

\(\Leftrightarrow x+\dfrac{2}{3}=\dfrac{2}{3}\)

\(\Leftrightarrow x=\dfrac{2}{3}-\dfrac{2}{3}=0\)

\(d)x+\dfrac{4}{5}=\dfrac{6}{20}-\dfrac{-7}{3}\)

⇔\(x+\dfrac{4}{5}=\dfrac{79}{30}\)

⇔\(x=\dfrac{79}{30}-\dfrac{4}{5}=\dfrac{11}{6}\)

tớ 0 biết làm

9. Tìm x biết 

a x- ( 12- 15)= -8

<=> x - 12 + 15 = -8

<=> x + 3 = -8

<=> x = -11

Vậy x = -11

b. (x- 29 )- ( 17- 38)= -9

<=> x - 29 - 17 + 38 = -9

<=> x - 8 = -9

<=> x = -1

Vậy x = -1

a) x-12+15=-8

=>x=-8-15+12

=>x=-11

Vậy x=-11

b)x-29+21=-9

=>x=-9-21+29

=>x=-1

Vậy x=-1

a) Ta có: x-(12-15)=-8

\(\Leftrightarrow x-12+15=-8\)

\(\Leftrightarrow x+3=-8\)

hay x=-8-3=-11

Vậy: x=-11

b) Ta có: \(\left(x-29\right)-\left(17-38\right)=-9\)

\(\Leftrightarrow x-29-17+38+9=0\)

\(\Leftrightarrow x+1=0\)

hay x=-1

Vậy: x=-1

a) 6 . x - 15 = 15

6 . x = 15 + 15

6 . x = 30

x = 30 : 6

x = 5

b) 2 . x + 3 = 9

2 . x = 9 - 3

2 . x = 6

x = 6 : 2

x = 3

c) 17 - 6 : x = 15

6 : x = 17 - 15

6 : x = 2

x = 6 : 2

x = 3

d) x : 3 + 12 = 14

x : 3 = 14 - 12

x : 3 = 2

x = 2 . 3

x = 6

a) 6 . x -15 = 15 

⇒ 6 .x = 15 + (-15)

⇒ 6 .x = 0

⇔ x = 0

Vậy x = 0.

b) 2.x + 3 = 9 

⇒2.x = 9 -3 

⇒  2.x = 6

⇔ x = 3

Vậy x = 3.

\(a)\)\(6-\left(15+15\right)=x-\left(15-6\right)\)

\(\Leftrightarrow6-30=x-9\)

\(\Leftrightarrow-24=x-9\)

\(\Leftrightarrow x=-24+9\)

\(\Leftrightarrow x=-15\)

Vậy\(x=-15\)

\(b)\)\(x+\frac{4}{12}=\frac{3}{-9}\)

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

\(\Leftrightarrow x=-\frac{1}{3}-\frac{1}{3}\)

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

Vậy\(x=\frac{-2}{3}\)

Linz

a, \(6-\left(15+15\right)=x-\left(15-6\right)\)

\(\Leftrightarrow6-30=x-9\Leftrightarrow15=x+30\Leftrightarrow x=-15\)

b, \(\frac{x+4}{12}=\frac{3}{-9}\)

\(\Leftrightarrow-9x-36=36\Leftrightarrow-9x=72\Leftrightarrow x=-8\)