mình không biết cái này bác mình đưa cho mình cái đề nên mình không biết trang mấy nữa 

a) Ta có: \(7-\left(2x+4\right)=-\left(x+4\right)\)

\(\Leftrightarrow7-2x-4=-x-4\)

\(\Leftrightarrow-2x+3+x+4=0\)

\(\Leftrightarrow-x+7=0\)

\(\Leftrightarrow-x=-7\)

hay x=7

Vậy: S={7}

b) Ta có: \(\dfrac{2+x}{5}-0.5x=\dfrac{1-2x}{4}+0.25\)

\(\Leftrightarrow\dfrac{4\left(2+x\right)}{20}-\dfrac{0.5x\cdot20}{20}=\dfrac{5\left(1-2x\right)}{20}+\dfrac{20\cdot0.25}{20}\)

\(\Leftrightarrow4\left(2+x\right)-10x=5\left(1-2x\right)+5\)

\(\Leftrightarrow8+4x-10x=5-10x+5\)

\(\Leftrightarrow-6x+8=-10x+10\)

\(\Leftrightarrow-6x+8+10x-10=0\)

\(\Leftrightarrow4x-2=0\)

\(\Leftrightarrow4x=2\)

hay \(x=\dfrac{1}{2}\)

Vậy: \(S=\left\{\dfrac{1}{2}\right\}\)

d) Ta có: \(\dfrac{x-1}{59}+\dfrac{x-2}{58}+\dfrac{x-3}{57}=\dfrac{x-59}{1}+\dfrac{x-58}{2}+\dfrac{x-57}{3}\)

\(\Leftrightarrow\dfrac{x-1}{59}-1+\dfrac{x-2}{58}-1+\dfrac{x-3}{57}-1=\dfrac{x-59}{1}-1+\dfrac{x-58}{2}-1+\dfrac{x-57}{3}-1\)

\(\Leftrightarrow\dfrac{x-60}{59}+\dfrac{x-60}{58}+\dfrac{x-60}{57}=\dfrac{x-60}{1}+\dfrac{x-60}{2}+\dfrac{x-60}{3}\)

\(\Leftrightarrow\left(x-60\right)\left(\dfrac{1}{59}+\dfrac{1}{58}+\dfrac{1}{57}\right)-\left(x-60\right)\left(1+\dfrac{1}{2}+\dfrac{1}{3}\right)=0\)

\(\Leftrightarrow\left(x-60\right)\left(\dfrac{1}{59}+\dfrac{1}{58}+\dfrac{1}{57}-1-\dfrac{1}{2}-\dfrac{1}{3}\right)=0\)

mà \(\dfrac{1}{59}+\dfrac{1}{58}+\dfrac{1}{57}-1-\dfrac{1}{2}-\dfrac{1}{3}\ne0\)

nên x-60=0

hay x=60

Vậy: S={60}

\(\dfrac{x}{y}=\dfrac{2}{7}\Rightarrow\dfrac{x}{2}=\dfrac{y}{7}=\dfrac{3x}{6}=\dfrac{5y}{35}\)

Áp dụng t/c...

\(\dfrac{x}{2}=\dfrac{y}{7}=\dfrac{3x}{6}=\dfrac{5y}{35}=\dfrac{-3x+5y}{-6+35}=\dfrac{58}{29}=2\\ \Rightarrow\left\{{}\begin{matrix}x=4\\y=14\end{matrix}\right.\)

\(\dfrac{x}{y}=\dfrac{2}{7}\Rightarrow\dfrac{x}{2}=\dfrac{y}{7}\)

Áp dụng tính chất dãy tỉ số bằng nhau ta có:

\(\dfrac{x}{2}=\dfrac{y}{7}\Rightarrow\dfrac{-3x+5y}{-6+35}=\dfrac{58}{29}=2\)

\(\dfrac{x}{2}=2\Rightarrow x=4\\ \dfrac{y}{7}=2\Rightarrow y=14\)

\(\dfrac{x}{y}=\dfrac{2}{7}\Rightarrow\dfrac{y}{7}=\dfrac{x}{2}\Rightarrow\dfrac{5y}{35}=\dfrac{-3x}{-6}\)

Áp dụng t/c của dãy số bằng nhau, ta có: \(\dfrac{5y+\left(-3x\right)}{35+\left(-6\right)}=\dfrac{58}{29}=2\)

\(\dfrac{y}{7}=2\Rightarrow y=14\)

\(\dfrac{x}{2}=2\Rightarrow x=4\)

\(\dfrac{15}{13}\)

Mng oi câu b 1202⁰ nha mng

Bài 1: 

a, 58.32 + 58.68 - 800

= 58.(32 + 68) - 800

= 58.100 - 800

= 5800 - 800

= 5000

b, 12020 + 280 : [55 - (7 - 4)³]

  =  12020 + 280 : [ 55 - 3³ ]

  =  12020 + 280 : [ 28]

  = 12020 + 10

  = 12030 

c, (96 - 19 - 45) - (55 + 96 - 119)

  = 96 - 19 - 45 - 55 - 96 + 119

 = (96 - 96) + (119 - 19) - (45 + 55)

= 0 + 100 - 100

= 0 

Bài 2:

a,7\(x\) - 70  = 105

   7\(x\)         = 105 + 70

   7\(x\)         = 175

     \(x\)          = 175 : 7

    \(x\)           = 25

A.x=11

B.=47

\(a,\Rightarrow7\left(x-5\right)=100-58=42\\ \Rightarrow x-5=6\\ \Rightarrow x=11\\ b,=5\cdot9-2^5:2^4=45-2=43\)

x²-14x+9y²-42y+107