2/5.1/3-2/15:1/5+3/5.1/3

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

= 2/15 - 2/75 + 1/5

= 23/75

\(\frac{23}{75}\)
 

= 23 / 75 k đi

giúp mk với

. là dấu gì vậy bạn

\(\frac{2}{5}.\frac{1}{3}-\frac{2}{15}:\frac{1}{5}+\frac{3}{5}.\frac{1}{3}\)

\(=\left(\frac{2}{5}.\frac{1}{3}\right)-\left(\frac{2}{15}:\frac{1}{5}\right)+\left(\frac{3}{5}.\frac{1}{3}\right)\)

\(=\frac{2}{15}-\frac{2}{75}+\frac{1}{5}\)

\(=\frac{23}{75}\)

\(\frac{2}{5}:\frac{1}{3}-\frac{2}{15}:\frac{1}{5}+\frac{3}{5}.\frac{1}{3}\)

\(=\frac{6}{5}+\frac{-2}{3}+\frac{1}{5}\)

\(=\frac{11}{15}\)

~ Hok tốt ~

\(\frac{4}{2.4}+\frac{4}{4.6}+\frac{4}{6.8}+...+\frac{4}{2008.2010}\)

\(=4.\left(\frac{1}{2.4}+\frac{1}{4.6}+\frac{1}{6.8}+...+\frac{1}{2008.2010}\right)\)

\(=4.\left(\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+...+\frac{1}{2008}-\frac{1}{2010}\right)\)

\(=4.\left[\frac{1}{2}+\left(\frac{1}{4}-\frac{1}{4}\right)+\left(\frac{1}{6}-\frac{1}{6}\right)+\left(\frac{1}{8}-\frac{1}{8}\right)+...+\left(\frac{1}{2008}-\frac{1}{2008}\right)-\frac{1}{2010}\right]\)

\(=4.\left[\frac{1}{2}-\frac{1}{2010}\right]\)

\(=4.\frac{502}{1005}=\frac{2008}{1005}\)

~ Hok tốt ~

b, \(\frac{4}{2.4}+\frac{4}{4.6}+\frac{4}{6.8}+...+\frac{4}{2008.2010}\)

\(=2\left(\frac{2}{2.4}+\frac{2}{4.6}+\frac{2}{6.8}+...+\frac{2}{2008.2010}\right)\)

\(=2\left(\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+...+\frac{1}{2008}-\frac{1}{2010}\right)\)

\(=2\left(\frac{1}{2}-\frac{1}{2010}\right)\)

\(=2.\frac{502}{1005}\)

\(=\frac{1004}{1005}\)

Study well ! >_<

cho mình xin đề bài

\(\dfrac{-2}{5}\cdot\dfrac{5}{6}+\dfrac{-2}{5}\cdot\dfrac{1}{6}-2\dfrac{3}{5}\)
\(=\dfrac{-2}{5}\left(\dfrac{5}{6}+\dfrac{1}{6}\right)-\dfrac{13}{5}\)
\(=\dfrac{-2}{5}\cdot1-\dfrac{13}{5}\)
\(=\dfrac{-2}{5}-\dfrac{13}{5}\)
\(=-3\)

chỗ cuối là sao vậy bạn

2  3/5

x-2/3=-1/2