(x+1/5) -4 = -2

x= -6-1/5

x= -31/5

Ta có : \(\left(2x+3\right)\left(x-7\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}2x+3=0\\x-7=0\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}2x=-3\\x=7\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}x=-\frac{3}{2}\\x=7\end{cases}}\)

Tìm x,biết :

\(a,\left(x+\frac{1}{5}\right)-4=-2\) 

\(\left(x+\frac{1}{5}\right)=2\)  

\(x+\frac{1}{5}=2\) 

\(x=\frac{9}{5}\) 

b,\(\left(2x+3\right)\left(x-7\right)=0\) 

\(\Rightarrow\orbr{\begin{cases}2x+3=0\\x-7=0\end{cases}}\) 

\(\Rightarrow\orbr{\begin{cases}x=-\frac{3}{2}\\x=7\end{cases}}\) 

\(c,\frac{31}{9}x-\frac{5}{2}=\frac{8}{3}\) 

\(\frac{31}{9}x=\frac{8}{3}+\frac{5}{2}\) 

\(\frac{31}{9}x=\frac{31}{6}\) 

\(x=\frac{3}{2}\)

\(a,x-7\frac{5}{8}=1\frac{1}{4}\)

=> \(x-\frac{61}{8}=\frac{5}{4}\)

=> \(x=\frac{5}{4}+\frac{61}{8}\)

=> \(x=\frac{10}{8}+\frac{61}{8}=\frac{71}{8}=8\frac{7}{8}\)

\(b,x+7\frac{5}{8}=9\frac{1}{4}\)

=> \(x+\frac{43}{5}=\frac{37}{4}\)

=> \(x=\frac{37}{4}-\frac{43}{5}=\frac{13}{20}\)

\(c,\left[x-7\frac{5}{8}\right]:\frac{1}{2}=3\)

=> \(\left[x-\frac{61}{8}\right]=3\cdot\frac{1}{2}\)

=> \(\left[x-\frac{61}{8}\right]=\frac{3}{2}\)

=> \(x-\frac{61}{8}=\frac{3}{2}\)

=> \(x=\frac{3}{2}+\frac{61}{8}=\frac{12}{8}+\frac{61}{8}=\frac{73}{8}=9\frac{1}{8}\)

d, \(\frac{x}{1\cdot3}+\frac{x}{3\cdot5}+\frac{x}{5\cdot7}+...+\frac{x}{97\cdot99}=99\)

=> \(\frac{x}{2}\left[\frac{2}{1\cdot3}+\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+...+\frac{2}{97\cdot99}\right]=99\)

=> \(\frac{x}{2}\left[1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{97}-\frac{1}{99}\right]=99\)

=> \(\frac{x}{2}\left[1-\frac{1}{99}\right]=99\)

=> \(\frac{x}{2}\cdot\frac{98}{99}=99\)

=> \(\frac{98x}{198}=99\)

=>  98x = 99 . 198

=> 98x = 19602

=> x = 19602 : 98 = 9801/49

a) \(x-7\frac{5}{8}=1\frac{1}{4}\)

=> \(x=\frac{5}{4}+\frac{61}{8}\)

=> \(x=\frac{71}{8}\)

b) \(x+7\frac{5}{8}=9\frac{1}{4}\)

=> \(x=\frac{37}{4}-\frac{61}{8}\)

=> \(x=\frac{13}{8}\)

c) \(\left(x-7\frac{5}{8}\right):\frac{1}{2}=3\)

=> \(x-\frac{61}{8}=3.\frac{1}{2}\)

=> \(x-\frac{61}{8}=\frac{3}{2}\)

=> \(x=\frac{3}{2}+\frac{61}{8}\)

=> \(x=\frac{73}{8}\)

d) \(\frac{x}{1.3}+\frac{x}{3.5}+...+\frac{x}{97.99}=99\)

=> \(x.\frac{1}{2}.\left(\frac{2}{1.3}+\frac{2}{3.5}+...+\frac{2}{97.99}\right)=99\)

=> \(\frac{1}{2}x\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+....+\frac{1}{97}-\frac{1}{99}\right)=99\)

=> \(x\left(1-\frac{1}{99}\right)=99:\frac{1}{2}\)

=> \(x.\frac{98}{99}=198\)

=> \(x=198:\frac{98}{99}=\frac{9801}{49}\)

\(b,\text{ }x+7\frac{5}{8}=9\frac{1}{4}\)

\(x=9\frac{1}{4}-\left(7+\frac{5}{8}\right)\)

\(x=9+\frac{1}{4}-7-\frac{5}{8}\)

\(x=\left(9-7\right)+\left(\frac{1}{4}-\frac{5}{8}\right)\)

\(x=2+-\frac{3}{8}\)

\(x=2\frac{-3}{8}\)

Ta có : ( x+1 ) + ( x + 2 ) + ( x + 3 ) + ( x + 4 ) + ( x + 5 ) = 30

            ( x + x + x +x +x ) + ( 1 + 2 + 3 + 4 + 5 ) = 30

             x * 5 + 15 = 30

              x * 5 = 30 - 15

              x * 5 = 15

                   x = 15 : 5 

                  x = 3

Vậy x = 3

Duyệt đi , chúc bạn học giỏi

(x + 1) + (x + 2) + (x + 3) + (x + 4) + (x + 5) = 4 + 5 + 6 + 7 + 8

x + 1 + x + 2 + x + 3 + x + 4 + x + 5 = 30

\(x\)x 5  + 15 = 30

\(x\)x 5 = 30 - 15 = 15

x = 15 : 5 = 3

a)15/8+3/4-5/12

=45+18-10/24

=53/24

b)11/24.12/33+5/6

=11.12/12.2.11.3+5/6

=1/6+5/6

=6/6=1

c)15/8+7/24:5/8

=15/8+7/24.8/5

=15/8+7.8/3.8.5

=15/8+7/15

=đề sai, nếu đúng thì như này

=8/15+7/15

=15/15=1

hbhvgvvggvgbhhgvbnj

a) \(\dfrac{x}{15}\)=\(\dfrac{x-2}{30}\)

=>30x=15 (x-2)

=>30x=15x-30

=>30x-15x=-30

=>15x =-30

=>x =-2

b)\(\dfrac{7}{8}\)<\(\dfrac{x}{80}\)<\(\dfrac{9}{10}\)

=>\(\dfrac{70}{80}\)<\(\dfrac{x}{80}\)<\(\dfrac{72}{80}\)

=> 70<x<72

=>x=71

c)\(\dfrac{1}{6}\)<\(\dfrac{5}{x}\)<\(\dfrac{1}{4}\)

=>\(\dfrac{5}{30}\)<\(\dfrac{5}{x}\)<\(\dfrac{5}{20}\)

=>20<x<30

=>x={21;22;23;24;25;26;27;28;29}

a)

\(\dfrac{2}{3}\cdot x-\dfrac{4}{7}=\dfrac{1}{8}\\ \dfrac{2}{3}\cdot x=\dfrac{1}{8}+\dfrac{4}{7}\\ \dfrac{2}{3}\cdot x=\dfrac{39}{56}\\ x=\dfrac{39}{56}:\dfrac{2}{3}\\ x=\dfrac{117}{112}\)

b)

\(\dfrac{2}{7}-\dfrac{8}{9}\cdot x=\dfrac{2}{3}\\ \dfrac{8}{9}\cdot x=\dfrac{2}{7}-\dfrac{2}{3}\\ \dfrac{8}{9}\cdot x=-\dfrac{8}{21}\\ x=-\dfrac{8}{21}:\dfrac{8}{9}\\ x=-\dfrac{3}{7}\)

c)

\(\dfrac{4}{7}+\dfrac{5}{9}:x=\dfrac{1}{5}\\ \dfrac{5}{9}:x=\dfrac{1}{5}-\dfrac{4}{7}\\ \dfrac{5}{9}:x=-\dfrac{13}{35}\\ x=\dfrac{5}{9}:\left(-\dfrac{13}{35}\right)\\ x=-\dfrac{175}{117}\)

Lấy máy tính ra ấn là đc mà bạn

A.

\(\dfrac{2}{3}x-\dfrac{4}{7}=\dfrac{1}{8}\)

<=>\(\dfrac{2}{3}x=\dfrac{1}{8}+\dfrac{4}{7}\)

<=>\(\dfrac{2}{3}x=\dfrac{39}{56}\)

<=> \(\dfrac{2}{3}x.\dfrac{3}{2}=\dfrac{39}{56}.\dfrac{3}{2}\)

<=> x= \(\dfrac{117}{112}\)

B.

\(\dfrac{2}{7}-\dfrac{8}{9}x=\dfrac{2}{3}\)

<=> \(\dfrac{-8}{9}x=\dfrac{2}{3}-\dfrac{2}{7}\)

<=> \(\dfrac{-8}{9}x=\dfrac{8}{21}\)

<=> \(\dfrac{-8}{9}x.\dfrac{-9}{8}=\dfrac{8}{21}.\dfrac{-9}{8}\)

<=> x= \(\dfrac{-3}{7}\)

C.

\(\dfrac{4}{7}+\dfrac{5}{9}:x=\dfrac{1}{5}\)

\(\dfrac{5}{9}:x=\dfrac{1}{5}-\dfrac{4}{7}\)

<=>\(\dfrac{5}{9}.\dfrac{1}{x}=\dfrac{-13}{35}\)

<=> \(\dfrac{5}{9x}=\dfrac{-13}{35}\)

<=> 9x= \(\dfrac{5.35}{-13}\)

<=> 9x = \(\dfrac{-175}{13}\)

<=> \(9x.\dfrac{1}{9}=\dfrac{-175}{13}.\dfrac{1}{9}\)

<=> x= \(\dfrac{-175}{117}\)