\(\dfrac{4}{5}\text{×}\dfrac{5}{6}\) =
có cách chình bày
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\(=\dfrac{102}{5}\cdot\dfrac{6}{5}-\dfrac{107}{3}\cdot\dfrac{6}{5}-\dfrac{3}{4}\)
\(=\dfrac{6}{5}\cdot\dfrac{-229}{15}-\dfrac{3}{4}\)
\(=\dfrac{-458}{25}-\dfrac{3}{4}=-\dfrac{1907}{100}\)
= 102/5 x 6/5 - 107/3 x 6/5 - 3/4
= 6/5 x ( 102/5 - 107/3 ) - 3/4
= 6/5 x -229/15 - 3/4
= -458/25 - 3/4
= -1907/100
![](https://rs.olm.vn/images/avt/0.png?1311)
Lời giải:
Gọi tích trên là $A$. Ta có:
$A=\frac{1}{2}\times \frac{2}{3}\times \frac{3}{4}\times \frac{4}{5}\times \frac{5}{6}$
$=\frac{1\times 2\times 3\times 4\times 5}{2\times 3\times 4\times 5\times 6}=\frac{1}{6}$
![](https://rs.olm.vn/images/avt/0.png?1311)
\(A=29\dfrac{1}{2}\cdot\dfrac{2}{3}+39\dfrac{1}{3}\cdot\dfrac{3}{4}+\dfrac{5}{6}\)
\(=\dfrac{59}{2}\cdot\dfrac{2}{3}+\dfrac{118}{3}\cdot\dfrac{3}{4}+\dfrac{5}{6}\)
\(=\dfrac{59}{3}+\dfrac{118}{4}+\dfrac{5}{6}\)
\(=\dfrac{59}{3}+\dfrac{59}{2}+\dfrac{5}{6}\)
\(=59\cdot\left(\dfrac{1}{3}+\dfrac{1}{2}\right)+\left(\dfrac{1}{3}+\dfrac{1}{2}\right)\)
\(=\dfrac{5}{6}\cdot\left(59+1\right)=\dfrac{5}{6}\cdot60=50\)
![](https://rs.olm.vn/images/avt/0.png?1311)
`a)1/7xx2/7+1/7xx5/7+6/7`
`=1/7xx(2/7+5/7)+6/7`
`=1/7xx1+6/7`
`=1/7+6/7=1`
`b)6/11xx4/9+6/11xx7/9-6/11xx2/9`
`=6/11xx(4/9+7/9-2/9)`
`=6/11xx9/9`
`=6/11`
Sorry nãy ghi thiếu.
`c)4/25xx5/8xx25/4xx24`
`=(4xx5xx25xx24)/(25xx8xx4)`
`=(4xx5xx24)/(4xx8)`
`=(5xx24)/8`
`=5xx3=15`
nhân vào vs nhau dc mà ??
20/30 = 2/3