a) ( 1/2-1/3-1/6).(1/2+2/3+3/4+...+2017/2018) + 3/4.x = 9/10

0.(1/2+2/3+3/4+...+2017/2018) + 3/4.x = 9/10

0+3/4.x = 9/10

3/4.x = 9/10

x = 9/10: 3/4

x = 6/5

b) x + ( 3/1.3+3/3.5+...+3/13.15) = 11/5

x + 3/2. ( 1-1/3 + 1/3 - 1/5 + ...+ 1/13 - 1/15) = 11/5

x + 3/2. ( 1-1/15) = 11/5

x + 3/2.14/15 = 11/5

x + 7/5 = 11/5

x = 11/5 - 7/5

x = 4/5

..... là gì?

a) ( 1/2-1/3-1/6).(1/2+2/3+3/4+...+2017/2018) + 3/4.x = 9/10

0.(1/2+2/3+3/4+...+2017/2018) + 3/4.x = 9/10

0+3/4.x = 9/10

3/4.x = 9/10

x = 9/10: 3/4

x = 6/5

b) x + ( 3/1.3+3/3.5+...+3/13.15) = 11/5

x + 3/2. ( 1-1/3 + 1/3 - 1/5 + ...+ 1/13 - 1/15) = 11/5

x + 3/2. ( 1-1/15) = 11/5

x + 3/2.14/15 = 11/5

x + 7/5 = 11/5

x = 11/5 - 7/5

x = 4/5

a) -12.(x - 5) + 7(3 - x) = 5

=> -12x + 60 + 21 - 7x = 5

=> -19x + 81 = 5

=> -19x = 5 - 81

=> -19x = -76

=> x = -76 : (-19)

=> x = 4

b) (x + 1) + (x + 2) + (x + 3) + ... + (x + 20) = 250

=> (x + x + x + ... + x) + (1 + 2 + 3 + ... + 20) = 250

=> 20x + 210 = 250

=> 20x = 250 - 210

=> 20x = 40

= > x = 40 : 20

=> x = 2

\(-12\left(x-5\right)+7\left(3-x\right)=5\)

\(\Leftrightarrow-12x+60+21-7x=5\)

\(\Leftrightarrow-19x+81=5\)

\(\Leftrightarrow81-5=19x\)

\(\Leftrightarrow19x=76\)

\(\Leftrightarrow x=4\)

\(\left(x+1\right)+\left(x+2\right)+\left(x+3\right)+...+\left(x+20\right)=250\)

\(\Leftrightarrow20x+\left(1+2+3+...+20\right)=250\)

\(\Leftrightarrow20x+\frac{20\left(20+1\right)}{2}=250\)

\(\Leftrightarrow20x+210=250\)

\(\Leftrightarrow20x=40\)

\(\Leftrightarrow x=2\)

\(6\cdot x-5=613\)

     \(6\cdot x=613+5\)

     \(6\cdot x=618\)

          \(x=618\div6\)

          \(x=103\)

Vậy \(x=103\)

\(12\cdot x+3\cdot x=30\)

\(x\cdot\left(12+3\right)=30\)

              \(x\cdot15=30\)

                    \(x=30\div15\)

                    \(x=2\)

Vậy \(x=2\)

\(125-25\cdot\left(x-1\right)=100\)

              \(25\cdot\left(x-1\right)=125-100\)

              \(25\cdot\left(x-1\right)=25\)

                        \(x-1=25\div25\)

                        \(x-1=1\)

                                 \(x=1+1\)

                                 \(x=2\)

Vậy \(x=2\)

\(\left(x-2\right)\cdot\left(x-14\right)=0\)

\(\Rightarrow\)  \(x-2=0\) hoặc \(x-14=0\)

TH1:  \(x-2=0\)                                 TH2: \(x-14=0\)

                 \(x=0+2\)                                          \(x=0+14\)        

                 \(x=2\)                                                   \(x=14\)

Vậy \(x=2\) hoặc \(x=14\)

\(128-3\cdot\left(x+4\right)=23\)

              \(3\cdot\left(x+4\right)=128-23\)

              \(3\cdot\left(x+4\right)=105\)

                      \(x+4=105\div3\)

                      \(x+4=35\)

                               \(x=35-4\)

                               \(x=31\)

Vậy \(x=31\)

12.x+3.x=30

x.(12+3)=30

x.15=30

x     =30:15

x     =2

125-25.(x-1)=100

      25.(x-1)=125-100

      25.(x-1)=25

          x-1=25:25

          x-1=1

          x   =1+1

          x=2

(x-2).(x-14)=0

x=14

128-3.(x+4)=23

      3.(x+4)=128-23

      3.(x+4)=105

         x+4=105:3

         x+4=35

         x   = 35+4

         x    =39

\(6x=618\Rightarrow x=103\)

\(x\left(12+3\right)=30\Rightarrow15x=30\Rightarrow x=2\)

\(25\left(x-1\right)=125-100=25\Rightarrow x-1=1\Rightarrow x=2\)

a) \(215+x=400\)

\(\Rightarrow x=400-215\)

\(\Rightarrow x=185\)

b) \(12,5-2x=\dfrac{1}{5}\)

\(\Rightarrow2x=12,5-\dfrac{1}{5}\)

\(\Rightarrow2x=\dfrac{123}{10}\)

\(\Rightarrow x=\dfrac{123}{10}:2\)

\(\Rightarrow x=\dfrac{123}{20}\)

còn câu c d nhanh cậu ơi

Bạn xem lại đề phần e nha .

\(c)x.0,25-\dfrac{3}{25}:x=2\dfrac{1}{4}\)

\(x.0,25-\dfrac{25}{3}.x=\dfrac{9}{4}\)

\(x.\left(0,25-\dfrac{25}{3}\right)=\dfrac{9}{4}\)

\(x.\dfrac{-97}{12}=\dfrac{9}{4}\)

\(x=\dfrac{-27}{97}\)

\(d)\left(x-\dfrac{1}{3}\right).\left(x-\dfrac{1}{4}\right)=0\)

Do : 2 số đó nhân với nhau bằng 0 nên một trong 2 số là số 0.

Do đó :

\(Th1:x-\dfrac{1}{3}=0\)

\(x=\dfrac{1}{3}\)

\(Th2:x-\dfrac{1}{4}=0\)

\(x=\dfrac{1}{4}\)

Ta có:

\(\left(\frac{1}{5}+\frac{1}{3}+\frac{3}{10}\right)+-\frac{1}{2}=\frac{1}{5}+\frac{1}{3}+\frac{3}{10}\)\(-\frac{1}{2}\)

=\(\frac{6}{30}+\frac{10}{30}+\frac{9}{30}-\frac{15}{30}=\frac{6+10+9-15}{30}=\frac{10}{30}=\frac{1}{3}\)

đơn giản 

......dễ.....

1,25.x-0,75.x=2.25-1

0.5.x=1.25

x=2,5

2.5 bàn nha

a,/x/=10\(\Rightarrow\hept{\begin{cases}x=-10\\x=10\end{cases}}\)

b,/x/=7\(\Rightarrow\hept{\begin{cases}x=-7\\x=7\end{cases}}\)

trang ơi bạn có làm đúng ko vậy

Đúng mà vì mk học rồi