a)\(\frac{72-x}{7}=\frac{x-70}{9}\)

<=>\(\frac{\left(72-x\right).9}{63}=\frac{\left(x-70\right).7}{63}\)

=>\(\frac{648-9x-7x+490}{63}=0\)

<=>.\(\frac{-16x+1138}{63}=0\)

<=>-16x+1138=0

<=>x=71,125

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

<=>\(\left(x-1\right)\left(x+3\right)=\left(x+2\right)\left(x-2\right)\)

<=>\(x^2+3x-x-3=x^2-4\)

<=>\(2x=-4+3\)

<=>\(2x=-1\)

<=>x=-0,5

a, 82-(15+x)=72

         15+x=82-72=10

              x=10-15

              x=-5

 b,(x-9).(x+2)=0

=>x-9=0 hoặc x+2=0

nếu x-9=0

=>   x  =0+9

=>   x  =9

nếu x+2=0

=>    x  =0-2

=>    x  =-2

vậy x=9 hoặc x=-2

tick nha

a.

82-(15+x)=72

(15+x)=82-72

15+x=10

x=10-15

x=-5

\(\frac{x-2}{12}+\frac{x-2}{20}+\frac{x-2}{30}+..+\frac{x-2}{72}=\frac{16}{9}\)

\(\Rightarrow\left(x-2\right).\left(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{72}\right)=\frac{16}{9}\)

\(\Rightarrow\left(x-2\right).\left(\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{8.9}\right)=\frac{16}{9}\)

\(\Rightarrow\left(x-2\right).\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{8}-\frac{1}{9}\right)=\frac{16}{9}\)

\(\Rightarrow\left(x-2\right).\left(\frac{1}{3}-\frac{1}{9}\right)=\frac{16}{9}\)

\(\Rightarrow x-2=0\Rightarrow x=2\)

sai rồi nha hoàng trung kiên

Ta có : 

\(\frac{x-2}{12}+\frac{x-2}{20}+\frac{x-2}{30}+\frac{x-2}{42}+\frac{x-2}{56}+\frac{x-2}{72}=\frac{16}{9}\)

\(\Leftrightarrow\)\(\left(x-2\right)\left(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}\right)=\frac{16}{9}\)

\(\Leftrightarrow\)\(\left(x-2\right)\left(\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}\right)=\frac{16}{9}\)

\(\Leftrightarrow\)\(\left(x-2\right)\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}\right)=\frac{16}{9}\)

\(\Leftrightarrow\)\(\left(x-2\right)\left(\frac{1}{3}-\frac{1}{9}\right)=\frac{16}{9}\)

\(\Leftrightarrow\)\(\left(x-2\right).\frac{2}{9}=\frac{16}{9}\)

\(\Leftrightarrow\)\(x-2=\frac{16}{9}:\frac{2}{9}\)

\(\Leftrightarrow\)\(x-2=\frac{16}{9}.\frac{9}{2}\)

\(\Leftrightarrow\)\(x-2=\frac{8}{1}.\frac{1}{1}\)

\(\Leftrightarrow\)\(x-2=8\)

\(\Leftrightarrow\)\(x=8+2\)

\(\Leftrightarrow\)\(x=10\)

Vậy \(x=10\)

Chúc bạn học tốt ~ 

a,

x-43+7=49-(50+3)

<=>x-36=49-53

<=>x-36=-4

<=>x=-4+36

<=>x=32

b

-(x-16)+70=45

<=>-x+16+70=45

<=>-x+86=45

<=>x=86-45

<=>x=41

Bài 2

a.,

2x-(-60)=3x-18

<=>2x+60=3x-18

<=>3x-2x=60+18

<=>x=78

b,

-45-5x=10-4x

<=>-4x+5x=-45-10

<=>x=-55

Nếu thấy bài làm của mình đúng thì tick nha bạn,mình xin chân thành cảm ơn.

a) x-  43 + 7 = 49 - (50 + 3)

x - 36 = -4

x = -4 + 36

x = 32

b) -(x - 16) + 70 = 45

-(x - 16) = -15

x - 16 = 15

x = 31

Bài 2:

2x - (-60) = 3x - 18

2x + 60 = 3x - 18

3x - 2x = 60 + 18

x = 78

b) -4- 5x = 10 - 4x

5x - 4x = -4 - 10

x = -14

Câu a bạn Mạnhlàm đúng rồi vậy mik làm câu b nhé

<br class="Apple-interchange-newline"><div id="inner-editor"></div>72−x7=x−709

<=>(72−x).963=(x−70).763

=>648−9x−7x+49063=0

<=>.−16x+113863=0

<=>-16x+1138=0

<=>x=71,125

a) theo đề bài ta có: x.x=0,16.9

=> x²=1,44

=> x²=a) theo đề bài ta có: x.x=0,16.9

=> x²=1,44

=> x²=(1,2)²

vậy x = 1,2

a) x:0,16=9:x                               b) 72-x/7=x-70/9

  => x.x=0,16.9                                 => 72+70/9=x+x/7

  => x²=1,44                                     => 718/9=x+x/7                           

  => x=1,2                                        => 718/9=x/1+x/7      

                                                       => 718/9=x.(1/1+1/7)

                                                       => 718/9=8/7x

                                                       => x=718/9: 8/7

                                                       => x= 2513/36

Viết lại 1 tí cho thuận mắt

Tức là: 7x + 9x - x - 5x = 290

                10x              = 290

                    x              = 290 : 10

                    x              = 29

\(x\times7+x\times9-x-x\times5=290\)

=> 7x + 9x - x - 5x = 290

=> 10x = 290

=> x = 290 : 10

=> x = 29

\(x\times7+x\times9-x-x\times5=290\)

          \(x\times\left(7+9-1-5\right)=290\)

                                      \(x\times10=290\)

                                                 \(x=290:10\)

                                                 \(x=29\)