|x|-1/4=6/18
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
Học sinh nhẩm và ghi:
24 : 6 = 4
18 : 6 = 4
60 : 6 = 10
6 : 6 = 1
6 x 4 = 24
6 x 3 = 18
6 x 10 = 60
6 x 1 = 6
(chú ý: nhận ra mối quan hệ giữa phép nhân và phép chia)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{1}{\left(x+5\right)\left(x+4\right)}+\frac{1}{\left(x+6\right)\left(x+5\right)}+\frac{1}{\left(x+6\right)\left(x+7\right)}=\frac{1}{18}\)
\(\Leftrightarrow\frac{1}{x+4}-\frac{1}{x+5}+\frac{1}{x+5}-\frac{1}{x+6}+\frac{1}{x+6}-\frac{1}{x+7}=\frac{1}{18}\)
\(\Leftrightarrow\frac{1}{x+4}-\frac{1}{x+7}=\frac{1}{18}\)
\(\Leftrightarrow\frac{\left(x+7\right)-\left(x+4\right)}{\left(x+7\right)\left(x+4\right)}=\frac{1}{18}\)
\(\Leftrightarrow\frac{3}{x^2+11x+28}=\frac{1}{18}\)
\(\Leftrightarrow x^2+11x+28=54\)
\(\Leftrightarrow x^2+11x=26\)
\(\Leftrightarrow x^2+11x-26=0\)
\(\Leftrightarrow\orbr{\begin{cases}x=2\\x=-13\end{cases}}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
`a)`
`6 \times 1 = 6`
`6 \times 4 = 24`
`6 \times 6 = 36`
`b)`
`12 \div 6 = 2`
`18 \div 6 = 3`
`48 \div 6 = 8`
`c)`
`6 \times 5 = 30`
`30 \div 6 = 5`
`30 \div 5 = 6`
![](https://rs.olm.vn/images/avt/0.png?1311)
5 x 6 = 30 2 x 6 = 12 3 x 6 = 18 4 x 6 = 24
6 x 5 = 30 6 x 2 = 12 6 x 3 = 18 6 x 4 = 24
![](https://rs.olm.vn/images/avt/0.png?1311)
1, x-72:36=18
x-2=18
=> x=20
2, \(\dfrac{x}{3}-\dfrac{1}{4}=\dfrac{-5}{6}\)
\(\dfrac{x}{3}=\dfrac{-7}{12}\)
12x= -21
->x= \(\dfrac{-21}{12}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
<=>|x|=7/12
<=>x=7/12 hoặc x=-7/12
\(\left|x\right|-\dfrac{1}{4}=\dfrac{6}{18}\)
\(\left|x\right|=\dfrac{6}{18}+\dfrac{1}{4}\)
\(\left|x\right|=\dfrac{42}{72}\)
\(x=\dfrac{42}{72}\)