6/10 và 5/10

56/126 và 81/126

15/30 và 20/30 và 18/30

\(\dfrac{1}{2};\dfrac{2}{3};\dfrac{3}{5}\left(MSC:30\right)\)

\(\dfrac{1}{2}=\dfrac{1\times15}{2\times15}=\dfrac{15}{30}\)

\(\dfrac{2}{3}=\dfrac{2\times10}{3\times10}=\dfrac{20}{30}\)

\(\dfrac{3}{5}=\dfrac{3\times6}{5\times6}=\dfrac{18}{30}\)

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?

`x - 3/3 = 4 - 1 - 2x/5`

`->` `x = (-5)`

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

=>5(x-3)=60-3(1-2x)

=>5x-15=60-3+6x

=>5x-15=6x+57

=>6x+57=5x-15

hay x=-72(nhận)

Bài 3 : 

b) Ta có 1+ 2 + 3 +4 + ...+ x =15

Nên \(\frac{x\left(x+1\right)}{2}=15\)

\(x\left(x+1\right)=30\)

=> \(x\left(x+1\right)=5.6\)

=> x = 5

Bài 2:

h; \(\dfrac{2}{3}\)\(x\)  + 50% + \(x\) = \(\dfrac{1}{10}\)

    \(\dfrac{2}{3}\)\(x\) + \(\dfrac{1}{2}\)  + \(x\) = \(\dfrac{1}{10}\)

    (\(\dfrac{2}{3}\)\(x\) + \(x\)) + \(\dfrac{1}{2}\) = \(\dfrac{1}{10}\)

     \(x\) \(\times\) (\(\dfrac{2}{3}\) + 1) + \(\dfrac{1}{2}\) = \(\dfrac{1}{10}\)

      \(x\) \(\times\) \(\dfrac{5}{3}\) + \(\dfrac{1}{2}\) = \(\dfrac{1}{10}\)

      \(x\) \(\times\) \(\dfrac{5}{3}\) = \(\dfrac{1}{10}\) - \(\dfrac{1}{2}\)

      \(x\) \(\times\) \(\dfrac{5}{3}\) = \(\dfrac{-2}{5}\)

      \(x\)         = \(\dfrac{-2}{5}\): \(\dfrac{5}{3}\)

      \(x\)         =   - \(\dfrac{6}{25}\) 

Lớp 5 chưa học số âm em nhé. 

a> x=13/12:2/3=13/8. vậy x=13/8

b>x=5/4 nhân 5/4=25/16. vậy...

c>x=7/4+1/2=9/4. vậy x=+-9/4

d>x=x=1-1/4=3/4. vậy...

a) \(0,5-\frac{2}{3}x=\frac{-7}{12}\)

\(\frac{1}{2}-\frac{2}{3}x=\frac{-7}{12}\)

\(\frac{2}{3}x=\frac{1}{2}-\frac{-7}{12}\)

\(\frac{2}{3}x=\frac{13}{12}\)

\(x=\frac{13}{12}:\frac{2}{3}\)

\(x=\frac{13}{8}\)

b) \(\frac{3}{4}-x:\frac{5}{4}=\frac{-1}{2}\)

\(x:\frac{5}{4}=\frac{3}{4}-\frac{-1}{2}\)

\(x:\frac{5}{4}=\frac{5}{4}\)

\(x=\frac{5}{4}.\frac{5}{4}\)

\(x=\frac{25}{16}\)

c) \(\left|x-\frac{1}{2}\right|-\frac{1}{4}=\frac{3}{2}\)

\(\left|x-\frac{1}{2}\right|=\frac{3}{2}+\frac{1}{4}\)

\(\left|x-\frac{1}{2}\right|=\frac{7}{4}\)

\(\Rightarrow\orbr{\begin{cases}x-\frac{1}{2}=\frac{7}{4}\\x-\frac{1}{2}=\frac{-7}{4}\end{cases}\Rightarrow\orbr{\begin{cases}x=\frac{9}{4}\\x=\frac{-5}{4}\end{cases}}}\)

Vậy x = 9/4 hoặc x = -5/4

d) \(\left|1-x\right|=\frac{1}{4}\)

\(\Rightarrow\orbr{\begin{cases}1-x=\frac{1}{4}\\1-x=\frac{-1}{4}\end{cases}\Rightarrow\orbr{\begin{cases}x=\frac{3}{4}\\x=\frac{5}{4}\end{cases}}}\)

Vậy x = 3/4 hoặc 5/4