\(a,x:\left(-\frac{15}{28}\right)=\frac{21}{35}\)

                      \(x=\frac{21}{35}\times\left(-\frac{15}{28}\right)\)

                       \(x=-\frac{9}{28}\)

\(b,x-\frac{1}{42}=-\frac{6}{7}\times\frac{5}{7}\)

    \(x-\frac{1}{42}=-\frac{30}{49}\)

                \(x=-\frac{30}{49}+\frac{1}{42}\)

                \(x=-\frac{173}{294}\)

\(c,\left(x-\frac{3}{4}\right):\frac{7}{5}=-\frac{1}{4}\)

               \(x-\frac{3}{4}=-\frac{1}{4}\times\frac{7}{5}\)

               \(x-\frac{3}{4}=-\frac{7}{20}\)

                           \(x=-\frac{7}{20}+\frac{3}{4}\)

                          \(x=\frac{2}{5}\)

a)x:-15/28=21/35

x=21/35.-15/28

x=-9/28

b)x-1/42= -6/7.5/7

x-1/42= -6/7.5/7

x-1/42=-30/49

x=-30/49+1/42

x=-173/294

c)(x-3/4):7/5=-1/4

x-3/4=-1/4.7/5

x-3/4=-7/20

x=-7/20+3/4

x=2/5

có gì sai xin tha thứ giùm nha!

hi hi!!!

a, x-[42+(-28)]=-8

x-14=-8

⇒x=(-8+14)=6

b, |x-3|=|5|+|-7|

|x-3|=5+7

|x-3|=12

TH1:x-3=12 TH2:x-3=-12

x=12+3 x=-12+3

⇒x=15 ⇒x=-9

Vậy x=15hoặc x=-9

xin lỗi b mình viết hơi sát bạn cố nhìn nha

Các bn ơi !Giúp mk đi!

Ai nhanh mk k nhé !

\(\left(7-x\right)-\left(25+7\right)=-25\Leftrightarrow7-x-25-7=-25\)

\(\Rightarrow\left(7-7\right)-x-25=-25\Rightarrow-x=\left(-25\right)+25=0\Rightarrow x=0 \)

\(x-\left[42+\left(-28\right)\right]=-8\Rightarrow x-\left(42-28\right)=-8\)

\(\Rightarrow x-14=-8\Leftrightarrow x=\left(-8\right)+14=6\)

\(|x-3|=|5|+|-7|\Rightarrow|x-3|=5+7=12\)

\(\Rightarrow\hept{\begin{cases}x-3=12\\x-3=-12\end{cases}}\Rightarrow\hept{\begin{cases}x=12+3=15\\x=\left(-12\right)+3=-9\end{cases}}\)

\(4-\left(7-x\right)=x-\left(13-4\right)\Rightarrow4-7+x=x-13+4\)

\(\Rightarrow\left(-3\right)+x=x-9\Leftrightarrow2x=\left(-3\right)-9=-12\Rightarrow x=-6\)

90 nha 

cái này mình k biết làm bạn ơi

a) x= \(\frac{-5}{12}\)

b) x = \(\frac{2}{5}\)

c) x =\(\frac{-87}{140}\)

d) x = \(\frac{109}{140}\)

e) x = \(\frac{13}{63}\)

Làm đầy đủ nha , mk thick cho , đừng viết kết quả 

a) \(\frac{11}{13}\)-  (\(\frac{5}{42}\)- X ) = -(\(\frac{15}{28}\)-\(\frac{11}{13}\))

    \(\frac{5}{42}\)- X =\(\frac{11}{13}\)+\(\frac{15}{28}\)-\(\frac{11}{13}\)

   \(\frac{5}{42}\)- X =\(\frac{15}{28}\)

                X = \(\frac{5}{42}\)-\(\frac{15}{28}\)

                X = \(\frac{-5}{12}\)

b) X + \(\frac{1}{3}\)= \(\frac{2}{5}\)- ( \(\frac{-1}{3}\))

    X +\(\frac{1}{3}\) = \(\frac{11}{15}\)

   X               = \(\frac{11}{15}\)-\(\frac{1}{3}\)

   X               = \(\frac{2}{5}\)

c) \(\frac{2}{3}\)X +\(\frac{5}{7}\)=\(\frac{3}{10}\)

    \(\frac{2}{3}\)X            = \(\frac{3}{10}\)-\(\frac{5}{7}\)

    \(\frac{2}{3}\)X            =\(\frac{-29}{70}\)

             X            = \(\frac{-29}{70}\): \(\frac{2}{3}\)

            X             = \(\frac{-87}{140}\)

d) \(\frac{3}{7}\)- X =\(\frac{1}{4}\)- (\(\frac{-3}{-5}\))

               X  = \(\frac{3}{7}\)-\(\frac{1}{4}\)+\(\frac{3}{5}\)

               X  = \(\frac{109}{140}\)

e) \(\frac{-21}{-13}\)X +\(\frac{1}{3}\)=\(\frac{-2}{-3}\)

   \(\frac{-21}{-13}\)X              = \(\frac{-2}{-3}\)-\(\frac{1}{3}\)

    \(\frac{-21}{-13}\)X            =\(\frac{1}{3}\)

                   X             = \(\frac{1}{3}\):\(\frac{-21}{-13}\)

                   X             = \(\frac{13}{63}\)

Hk tốt

1. a

\(\dfrac{8}{5}-\dfrac{5}{6}\cdot\dfrac{3}{4}\)

\(=\dfrac{8}{5}-\dfrac{5\cdot3}{3\cdot2\cdot4}\)

\(=\dfrac{8}{5}-\dfrac{5}{8}=\dfrac{39}{40}\)

1.b

\(=\dfrac{7}{8}+\dfrac{5}{6}\cdot\dfrac{3}{2}\)

\(=\dfrac{7}{8}+\dfrac{5\cdot3}{3\cdot2\cdot2}\)

\(=\dfrac{7}{8}+\dfrac{5}{4}=\dfrac{17}{8}\)

2.a

\(\dfrac{4}{5}+x=\dfrac{11}{10}\)

\(x=\dfrac{11}{10}-\dfrac{4}{5}=\dfrac{3}{10}\)

2.b

\(x-\dfrac{3}{4}=\dfrac{5}{7}\)

\(x=\dfrac{5}{7}+\dfrac{3}{4}=\dfrac{41}{28}\)