\(2^5=32;;;;;;;;;;;3^4=81\)

42+(3x+7):2=32+81

(3x+7):2=113-42

(3x+7):2=71

3x+7=71*2

3x+7=142

3x=142-7

3x=135

x=135:3

x=45

\(\dfrac{4}{x}=\dfrac{y}{21}=\dfrac{28}{49}=\dfrac{28:7}{49:7}=\dfrac{4}{9}\\ Vậy:x=\dfrac{4.9}{4}=9\\ y=\dfrac{4.21}{9}=\dfrac{28}{3}\)

\(\dfrac{x}{2}=\dfrac{3}{y}\\ \Leftrightarrow x.y=2.3=6\\ Vậy:\left[{}\begin{matrix}\left(x;y\right)=\left(1;6\right)=\left(6;1\right)\\\left(x;y\right)=\left(2;3\right)=\left(3;2\right)\end{matrix}\right.\)

\(3,\\ \dfrac{42}{54}=\dfrac{42:6}{54:6}=\dfrac{7}{9}\\ \dfrac{42}{54}=\dfrac{7}{x}=\dfrac{7}{9}\\ Vậy:x=\dfrac{7.9}{7}=9\)

\(\frac{2}{3}:\frac{x}{5}+\frac{5}{7}=\frac{2}{7}:\frac{3}{5}+\frac{10}{9}\)

\(\Rightarrow\frac{2}{3}:\frac{x}{5}+\frac{5}{7}=\frac{2}{7}.\frac{5}{3}+\frac{10}{9}\)

\(\Rightarrow\frac{2}{3}:\frac{x}{5}+\frac{5}{7}=\frac{10}{21}+\frac{10}{9}\)

\(\Rightarrow\frac{2}{3}:\frac{x}{5}+\frac{5}{7}=\frac{100}{63}\)

\(\Rightarrow\frac{2}{3}:\frac{x}{5}=\frac{100}{63}-\frac{5}{7}\)

\(\Rightarrow\frac{2}{3}:\frac{x}{5}=\frac{55}{63}\)

\(\Rightarrow\frac{x}{5}=\frac{2}{3}:\frac{55}{63}\)

\(\Rightarrow\frac{x}{5}=\frac{2}{3}.\frac{63}{55}\)

\(\Rightarrow\frac{x}{5}=\frac{42}{55}\)

\(\Rightarrow x=\frac{42.5}{55}=\frac{42}{11}\)

Nên ta chọn đáp án D là đáp án đúng! 

( trong bài có dấu . tức là dấu dấu nhân bn nhé )

2/3 : x/5 + 5/7 = 2/7 : 3/5 + 10/9

2/3 : x/5 + 5/7 = 10/21 + 10/9

2/3 : x/5 + 5/7 = 100/63

2/3 : x/5 = 100/63 - 5/7

2/3 : x/5 = 55/63

2/3 . 5/x= 55/63

=) 5/x = 55/63 : 2/3

=) 5/x = 55/42

ta có : a/b = c/d =) a.d=b.c

(=) 55.x = 5.42

      55.x = 210

=)        x = 210 : 55 = 42/11

vậy đáp án đúng là D

 chúc bn học tốt

1: \(\dfrac{x-1}{3}=\dfrac{y-2}{4}=\dfrac{z+7}{5}\)

mà x+y-z=8

nên Áp dụng tính chất của dãy tỉ số bằng nhau, ta được:

\(\dfrac{x-1}{3}=\dfrac{y-2}{4}=\dfrac{z+7}{5}=\dfrac{x-1+y-2-z-7}{3+4-5}=\dfrac{8-3-7}{2}=\dfrac{-2}{2}=-1\)

=>\(\left\{{}\begin{matrix}x-1=-1\cdot3=-3\\y-2=-1\cdot4=-4\\z+7=-1\cdot5=-5\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}x=-2\\y=-2\\z=-12\end{matrix}\right.\)

2: \(\dfrac{x+1}{3}=\dfrac{y+2}{-4}=\dfrac{z-3}{5}\)

mà 3x+2y=47-42=5

nên Áp dụng tính chất của dãy tỉ số bằng nhau, ta được:

\(\dfrac{x+1}{3}=\dfrac{y+2}{-4}=\dfrac{z-3}{5}=\dfrac{3x+3+2y+4}{3\cdot3+2\left(-4\right)}=\dfrac{5+7}{9-8}=12\)

=>\(\left\{{}\begin{matrix}x+1=12\cdot3=36\\y+2=-12\cdot4=-48\\z-3=12\cdot5=60\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}x=35\\y=-48-2=-50\\z=60+3=63\end{matrix}\right.\)

Ta có

42+(3x+7):2=2^5+3^4

<=>42+(3x+7):3=113

<=>(3x+7):2=71

<=>3x+7=71.2

<=>3x+7=142

<=>3x=142-7

<=>3x=135

<=>x=135:3

<=>x=45

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

42 + ( 3x + 7 ) : 2 = 2⁵ + 3⁴

=> 42 + ( 3x + 7 ) : 2 = 32 + 81

=> ( 3x + 7 ) : 2 = 32 + 81 - 42

=> ( 3x + 7 ) : 2 = 71

=> 3x + 7 = 71 . 2

=> 3x + 7 = 142

=> 3x = 142 - 7

=> 3x = 135

=> x = 135 : 3

=> x = 45

42 + (3x + 7) : 2 = 2⁵ + 3⁴

42 + (3x + 7) : 2 = 32 + 81

42 + (3x + 7) : 2 = 113

(3x + 7) : 2 = 113 - 42

(3x + 7) : 2 = 71

3x + 7 = 71 * 2

3x + 7 = 142

3x = 142 - 7

3x = 135

x = 135 : 3

x = 45 

1 , 10

2 , 8

3 , 5

4 , 2

5 , 1

6 ,

1/ `|x|=10<=> x=\pm 10`

2/ `|x-8|=0<=>x-8=0<=>x=8`

3/ `7+|x|=12<=>|x|=5<=>x=\pm 5`

4/ `|x+1|=3`

$\Leftrightarrow\left[\begin{array}{1}x+1=3\\x+1=-3\end{array}\right.\\\Leftrightarrow\left[\begin{array}{1}x=3\\x=-4\end{array}\right.$

5/ `15-x=16-(14-42)`

`<=>15-x=16+28`

`<=>15-x=44`

`<=>x=-29`

6/ `210-(x-12)=168`

`<=>210-x+12=168`

`<=>222-x=168`

`<=>x=54`

1.

\(\left|x\right|=10\Leftrightarrow x=\pm10\)

2.

\(\left|x-8\right|=0\Leftrightarrow x-8=0\Leftrightarrow x=8\)

3.

\(7+\left|x\right|=12\Leftrightarrow\left|x\right|=5\Leftrightarrow x=\pm5\)

1: x=3/4-1/2=3/4-2/4=1/4

2: x-1/5=2/11

=>x=2/11+1/5=21/55

3: x-5/6=16/42-8/56

=>x-5/6=8/21-4/28=5/21

=>x=5/21+5/6=15/14

4: x/5=5/6-19/30

=>x/5=25/30-19/30=6/30=1/5

=>x=1

5: =>|x|=1/3+1/4=7/12

=>x=7/12 hoặc x=-7/12

6: x=-1/2+3/4

=>x=3/4-1/2=1/4

11: x-(-6/12)=9/48

=>x+1/2=3/16

=>x=3/16-1/2=-5/16

1)x= 1/4

2)x= 2/11+ 1/5

   x= 21/55

3)x - 5/6 = 5/21

   x         = 5/21+5/6

   x         = 15/14

4)x/5 = 5/6 + -19/30

   x:5 = 1/5

   x    = 1/5.5

   x    = 1

5) |x| - 1/4 = 6/18

    |x|           = 6/18 - 1/4

    |x|            =7/12

⇒x= 7/12 hoặc -7/12

6)x = -1/2 +3/4

   x= 1/4

7) x/15 = 3/5 + -2/3

   x:15  = -1/15

  x        = -1/15. 15

  x        = -1

8)11/8 + 13/6 = 85/x  

       85/24      = 85/x

  ⇒      x           = 24

9) x - 7/8 = 13/12

   x          = 13/12 + 7/8

   x          = 47/24

10)x - -6/15 = 4/27  

     x            = 4/27 + (-6/15)

    x             = -34/135

11) -(-6/12)+x = 9/48

                    x= 9/48 - 6/12

                    x = -5/16

12) x - 4/6 = 5/25 + -7/15

      x -4/6  =  -4/15

     x           = -4/15 + 4/6

    x             = 2/5

a.-1,75-(-\(\dfrac{1}{9}\)-2\(\dfrac{1}{8}\))
-1,75-\(\dfrac{1}{9}+\dfrac{17}{8}\)
\(-\dfrac{7}{4}-\dfrac{1}{9}+\dfrac{17}{8}\)
\(\dfrac{-126}{72}-\dfrac{8}{72}+\dfrac{153}{72}\)
=\(\dfrac{19}{72}\)

b.\(\dfrac{-1}{12}-\left(2\dfrac{5}{8}-\dfrac{1}{3}\right)\)
\(\dfrac{-1}{12}-\left(\dfrac{21}{8}-\dfrac{1}{3}\right)\)
\(\dfrac{-1}{12}-\dfrac{21}{8}+\dfrac{1}{3}\)
\(\dfrac{-2}{24}-\dfrac{63}{24}+\dfrac{64}{24}\)
=\(\dfrac{-1}{24}\)

\(\dfrac{-5}{6}-\left(\dfrac{-3}{8}+\dfrac{1}{10}\right)\)
\(\dfrac{-5}{6}-\dfrac{-3}{8}-\dfrac{1}{10}\)