+ \(72:\left(x-15\right)=8\)

\(x-15=9\)

\(x=24\)

+ \(\dfrac{3}{90}-3x=3\)

\(3\left(\dfrac{1}{90}-x\right)=3\)

\(\dfrac{1}{90}-x=1\)

\(x=\dfrac{1}{90}-1=\dfrac{-89}{90}\)

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

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

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

1.4x - 5(-3+x)=7

   4x - 5(x-3)  =7

  4x - 5x + 15=7

     -1x   + 15=7

     -1x         =-8

       =>    x =8

2.5(x-3) - 2(x+6)=9

  5x - 15 -2x -12=9

 5x - 2x -15 - 12=9

             5x - 2x=9 + 12 + 15

             5x - 2x= 36

                3x   = 36

        =>     x   = 12

3.4(x-1) - 3(x-2)=15

  4x - 4 - 3x + 6=15

           4x - 3x =15 - 6 + 4

           4x - 3x = 13

              => x = 13

Nhớ mink nhoa pn

đây mà là toán lớp 1 à.đồ dở hơi.

ban a toán lớp mấy thì  toán vậy bạn có trả lời được ko mà còn ra vẻ hả bạn 'doraemi'

dúng rồi đó ko trả lời thì thôi 

7/8 + 3/4=13/8

3/2 + 4/5=23/10

6/7 * 5/6=5/7

5/6 : 8/9=15/16

\(\frac{7}{8}+\frac{3}{4}=\frac{28}{32}+\frac{24}{32}=\frac{52}{32}\)

\(\frac{3}{2}+\frac{4}{5}=\frac{15}{10}+\frac{8}{10}=\frac{23}{10}\)

\(\frac{6}{7}x\frac{5}{6}=\frac{30}{42}\)

\(\frac{5}{6}:\frac{8}{9}=\frac{5}{6}x\frac{9}{8}=\frac{45}{48}\)

\(\frac{7}{8}+\frac{3}{4}=\frac{13}{8}\)

\(\frac{3}{2}+\frac{4}{5}=\frac{23}{10}\)

\(\frac{6}{7}.\frac{5}{6}=\frac{5}{7}\)

\(\frac{5}{6}:\frac{8}{9}=\frac{15}{16}\)

a: =7/8:(2/9-18+1/36)-5/12

=-7/142-5/12=-397/852

b: =3/7(4/9+5/9:6/12)=2/3

c: =5^8(16/31-47/31)+1/3=-5^8+1/3

d: =7/2(3/8+5/8:4/15)=609/64

khỏi chép đề nha

a\Câu 1:

200 : ( 15 - x ) = 15 + 5

200 : ( 15 - x ) = 20

15 - x = 200 : 20

15 - x = 10

x = 15 - 10

x = 5

Câu 2:

63 : ( x - 5 ) = 22 -1

63 : ( x - 5 ) = 21

x - 5 = 63 : 21

x - 5 = 3

x = 3 + 5

x = 8

Câu 1:

\(\left(x-2\right)\left(x^2+2x+4\right)+25x=x\left(x+5\right)\left(x-5\right)+8\)

\(\Leftrightarrow x^3-8+25x=x\left(x^2-25\right)+8\)

\(\Leftrightarrow x^3-8+25x=x^3-25x+8\)

\(\Leftrightarrow x^3-8+25x-x^3+25x-8=0\)

\(\Leftrightarrow50x-16=0\)

\(\Leftrightarrow50x=16\)

\(\Leftrightarrow x=\dfrac{8}{25}\)

Câu 2 :

\(\dfrac{x+5}{4}+\dfrac{3+2x}{3}=\dfrac{6x-1}{3}-\dfrac{1-2x}{12}\)

<=> \(\dfrac{3\left(x+5\right)}{12}+\dfrac{4\left(3+2x\right)}{12}=\dfrac{4\left(6x-1\right)}{12}-\dfrac{1-2x}{12}\)

<=>\(\dfrac{3x+15+12+8x}{12}=\dfrac{24x-4-1+2x}{12}\)

<=> 3x + 15 + 12 + 8x = 24x - 4 - 1 +2x

<=> 11x+27 = 26x -5

<=> ( 26x - 5 ) - ( 11x + 27 ) = 0

<=> 15x - 32 = 0

<=> 15x = 32

<=> x = \(\dfrac{32}{15}\)

Câu 3:

x - 4/3 - 3x - 1/12 = 3x + 1/4 + 9x - 2/8

<=> 4x - 16 - 3x + 1/12 = 6x + 2 + 9x - 2/8

<=> x - 15/12 = 15x/8

<=> 8x - 120 = 180x

<=> 120 = -172x <=> x = -172/120 = -43/30