A, 34+(9-21)=3417-(x+3417)

  34 + (-12) = 3417 - x - 3417

   22 = ( 3417 - 3417 ) - x

   22 = 0 - x 

     x = 0 - 22

     x = -22

 Vậy: x = - 22

B,  (15-x)+(x-21)=7-(-8+x)

 15 - x + x - 21 = 7 + 8 - x

-x + x = 7 + 8 - x - 15 + 21

0 = 15 - x - 15 + 21 

0 = ( 15 - 15 ) - x + 21

0 = 0 - x + 21

-x = 0 - 0 - 21

- x = -21

x = 21

Vậy : x = 21

k mình nha, thank you!

\(\dfrac{-7}{x}=\dfrac{-21}{x}-34\)

\(\Rightarrow\dfrac{-7}{x}+\dfrac{21}{x}=-34\)

\(\Rightarrow\dfrac{14}{x}=-34\Rightarrow-34x=14\Rightarrow x=\dfrac{-7}{17}\)

tìm x a

e xin lỗi em ghi nhầm là lớp 7 chứ ko pk lớp 8 đâu ạ

uk tìm x 

a: \(=\dfrac{18}{51}\cdot\dfrac{34}{9}\cdot\dfrac{17}{18}=\dfrac{17}{51}\cdot\dfrac{34}{9}=\dfrac{1}{3}\cdot\dfrac{34}{9}=\dfrac{34}{27}\)

b: \(=\dfrac{21}{32}\cdot\dfrac{4}{7}\cdot25\cdot\dfrac{4}{5}=\dfrac{21}{7}\cdot\dfrac{4}{32}\cdot20=60\cdot\dfrac{1}{8}=\dfrac{15}{2}\)

\(\frac{7}{\left(x+3\right)\left(x+10\right)}+\frac{11}{\left(x+10\right)+\left(x+21\right)}+\frac{13}{\left(x+21\right)\left(x+34\right)}=\frac{x}{\left(x+3\right)\left(x+34\right)}\)

\(\frac{1}{x+3}-\frac{1}{x+10}+\frac{1}{x+10}-\frac{1}{x+21}+\frac{1}{x+21}-\frac{1}{x+34}=\frac{x}{\left(x+3\right)\left(x+34\right)}\)

\(\frac{1}{x+3}-\frac{1}{x+34}=\frac{x}{\left(x+3\right)\left(x+34\right)}\)

\(\frac{\left(x+34\right)-\left(x+3\right)}{\left(x+3\right)\left(x+34\right)}=\frac{x}{\left(x+3\right)\left(x+34\right)}\)

\(\frac{31}{\left(x+3\right)\left(x+34\right)}=\frac{x}{\left(x+3\right)\left(x+34\right)}\)

\(\Rightarrow x=31\)

\(\frac{7}{\left(x+3\right)\left(x+10\right)}+\frac{11}{\left(x+10\right)\left(x+21\right)}+\frac{13}{\left(x+21\right)\left(x+34\right)}=\frac{x}{\left(x+3\right)\left(x+34\right)}\)

\(\Leftrightarrow\frac{1}{x+3}-\frac{1}{x+10}+\frac{1}{x+10}-\frac{1}{x+21}+\frac{1}{x+21}-\frac{1}{x+34}=\frac{x}{\left(x+3\right)\left(x+34\right)}\)

\(\Leftrightarrow\frac{1}{x+3}-\frac{1}{x+34}=\frac{x}{\left(x+3\right)\left(x+34\right)}\)

\(\Leftrightarrow\frac{\left(x+34\right)-\left(x+3\right)}{\left(x+3\right)\left(x+34\right)}=\frac{x}{\left(x+3\right)\left(x+34\right)}\)

\(\Leftrightarrow x+34-x-3=x\)

\(\Leftrightarrow x=31\)

\(ĐKXĐ\): \(x\ne-3\); \(x\ne-10\); \(x\ne-21\); \(x\ne-34\)

\(\frac{7}{\left(x+3\right)\left(x+10\right)}+\frac{11}{\left(x+10\right)\left(x+21\right)}+\frac{13}{\left(x+21\right)\left(x+34\right)}=\frac{x}{\left(x+3\right)\left(x+34\right)}\)

\(\Leftrightarrow\frac{1}{x+3}-\frac{1}{x+10}+\frac{1}{x+10}-\frac{1}{x+21}+\frac{1}{x+21}-\frac{1}{x+34}=\frac{x}{\left(x+3\right)\left(x+34\right)}\)

\(\Leftrightarrow\frac{1}{x+3}-\frac{1}{x+34}=\frac{x}{\left(x+3\right)\left(x+34\right)}\)

\(\Leftrightarrow\frac{\left(x+34\right)-\left(x+3\right)}{\left(x+3\right)\left(x+34\right)}=\frac{x}{\left(x+3\right)\left(x+34\right)}\)

\(\Rightarrow\left(x+34\right)-\left(x+3\right)=x\)

\(\Leftrightarrow x+34-x-3=x\)

\(\Leftrightarrow x=31\)( thỏa mãn )

Vậy \(x=31\)

$-7\cdot(x+9)+(-21)=34$

$\Rightarrow -7\cdot(x+9)=34+21$

$\Rightarrow -7\cdot(x+9)=55$

$\Rightarrow x+9=\dfrac{55}{-7}$

$\Rightarrow x=\dfrac{-55}{7}-9$

$\Rightarrow x=\dfrac{-118}{7}$

\(b,\left(15-x\right)+\left(x-12\right)=7-\left(-8-x\right)\)

\(\Leftrightarrow15-x+x-12=7+8+x\)

\(\Leftrightarrow3=15+x\)

\(\Leftrightarrow x=3-15\)

\(\Leftrightarrow x=-12\)

Vậy : \(x=-12\)

Mik sửa lại câu a cho bạn Đạt này

A. 34 + (9 - 21)= 3417 - (x + 3417)

<=>34 + (-12) = 3417 - x - 3417

<=>22 = -x

=> x = -22

Vậy x= -22

\(a,34+\left(9-21\right)=3417-\left(x+3417\right)\)

\(\Leftrightarrow34+13=3417-x-3417\)

\(\Leftrightarrow47=-x\)

\(\Leftrightarrow x=-47\)

Vậy : \(x=-47\)