\(\frac{7}{3.13}+\frac{7}{13.23}+\frac{7}{23.33}+\frac{7}{33.43}\)

\(=\frac{7}{10}\left(\frac{10}{3.13}+\frac{10}{13.23}+\frac{10}{23.33}+\frac{10}{33.43}\right)\)

\(=\frac{7}{10}\left(\frac{1}{3}-\frac{1}{13}+\frac{1}{13}-\frac{1}{23}+\frac{1}{23}-\frac{1}{33}+\frac{1}{33}-\frac{1}{43}\right)\)

\(=\frac{7}{10}\left(\frac{1}{3}-\frac{1}{43}\right)\)

\(=\frac{7}{10}\left(\frac{43}{129}-\frac{3}{129}\right)\)

\(=\frac{7}{10}.\frac{40}{129}\)

\(=\frac{28}{129}\)

mk làm đúng rồi nha, ko tin bấm thử máy tính

 7/3.13 + 7/13.23 + 7/23.33 + 7/33.43

= 7/10.(1/3-1/13+1/13-1/23+1/23-1/33+1/33-1/43)

= 7/10.(1/3-1/43)

= 7/10 . 14/43

= 49/215

Đặt A ta có :

\(A=\frac{7}{3\times13}+\frac{7}{13\times23}+...+\frac{7}{53\times56}\)

\(A=\frac{7}{10}\times\left(\frac{10}{3\times13}+\frac{10}{13\times23}+...+\frac{10}{53\times56}\right)\)

\(A=\frac{7}{10}\times\left(\frac{1}{3}-\frac{1}{13}+\frac{1}{13}-\frac{1}{23}+...+\frac{1}{53}-\frac{1}{63}\right)\)

\(A=\frac{7}{10}\times\left(\frac{1}{3}-\frac{1}{63}\right)\)

\(A=\frac{7}{10}\times\frac{20}{63}\)

\(\Rightarrow A=\frac{2}{9}\)

\(\frac{1}{5}\)+\(\frac{4}{5}\): 5=\(\frac{5}{5}\): 5=1:5=\(\frac{1}{5}\)

Đ/S \(\frac{1}{5}\)

\(\frac{1}{5}+\frac{4}{5}:5=\frac{1}{5}+\frac{4}{5}.\frac{1}{5}=\frac{1}{5}+\frac{4}{25}=\frac{5}{25}+\frac{4}{25}=\frac{9}{25}\).

Chúc cậu hok tốt!

#Dũng

\(\frac{1}{5}+\frac{4}{5}:5=\frac{1}{5}+\frac{4}{25}=\frac{5+4}{25}=\frac{9}{25}\)

:):):):):):):):):):):):):):):):) mình đâu có biết!

\(A=\frac{7}{3.13}+\frac{7}{13.23}+...+\frac{7}{53.63}\)

\(A=7.\left(\frac{1}{3.13}+\frac{1}{13.23}+...+\frac{1}{53.63}\right)\)

\(10A=7.\left(\frac{10}{3.13}+\frac{10}{13.23}+...+\frac{10}{53.63}\right)\)

\(10A=7.\left(\frac{1}{3}-\frac{1}{63}\right)\)

\(10A=7.\frac{20}{63}\)

\(10A=\frac{20}{9}\)

\(A=\frac{20}{9}:10\)

\(A=\frac{20}{9}.\frac{1}{10}\)

\(A=\frac{2}{9}\)

Vậy A=\(\frac{2}{9}\)

Chúc bạn học tốt~

A = \(\frac{7}{3.13}\)\(+\)\(\frac{7}{13.23}\)\(+\)\(\frac{7}{23.33}\)\(+\)..........  \(+\)\(\frac{7}{53.63}\)

\(\Rightarrow\)A = 7 . (\(\frac{1}{3.13}\)\(+\)\(\frac{1}{13.23}\)\(+\)\(\frac{1}{23.33}\)\(+\)...... \(\frac{1}{53.63}\))

\(\Rightarrow\)A = \(\frac{1}{10}\). 7 . ( \(\frac{1}{3}\)\(-\)\(\frac{1}{13}\)\(+\)\(\frac{1}{13}\)\(-\)\(\frac{1}{23}\)\(+\)\(\frac{1}{23}\)\(-\)\(\frac{1}{33}\)\(+\)....... \(+\)\(\frac{1}{53}\)\(-\)\(\frac{1}{63}\))

\(\Rightarrow\)A = \(\frac{7}{10}\). ( \(\frac{1}{3}\)\(-\)\(\frac{1}{63}\))

\(\Rightarrow\)A = \(\frac{7}{10}\). \(\frac{20}{63}\)

\(\Rightarrow\)A = \(\frac{2}{9}\)

Chúc các anh em học tốt !!!

A=1/3-1/13+1/13-1/23+1/23-1/33+.........+1/53-1/63

=1/3-1/63

=21/63-1/63

=20/63

5/3.13 + 5/13.23 + 5/23,33

= 1,975373039 + 5/23,33

=2,18968937

bạn ơi mình = không

\(B=\frac{5}{3}.\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+....+\frac{1}{2014}-\frac{1}{2017}\right)\)

\(B=\frac{5}{3}.\left(1-\frac{1}{2017}\right)\)

\(B=\frac{5}{3}.\frac{2016}{2017}=\frac{10080}{6051}\)

\(B=\frac{5}{1.4}+\frac{5}{4.7}+...+\frac{5}{2014.2017}\)

\(3M=5\left(\frac{1}{1.4}+\frac{1}{4.7}+...+\frac{1}{2014.2017}\right)\)

\(3M=5\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+...+\frac{1}{2014}-\frac{1}{2017}\right)\)

\(3M=5\left(1-\frac{1}{2017}\right)\)

\(3M=5.\frac{2016}{2017}\)

\(3M=\frac{10080}{2017}\)

\(\Rightarrow M=\frac{3360}{2017}\)

Ta có: 

\(B=\frac{5}{1.4}+\frac{5}{4.7}+.....+\frac{5}{2014.2017}\)

\(\Rightarrow B.\frac{3}{5}=\frac{3}{1.4}+\frac{3}{4.7}+.....+\frac{3}{2014.2017}\)

\(=\left(1-\frac{1}{4}\right)+\left(\frac{1}{4}-\frac{1}{7}\right)+......+\left(\frac{1}{2014}-\frac{1}{2017}\right)\)

\(=1-\frac{1}{2017}\)

\(=\frac{2016}{2017}\)

\(\Rightarrow B=\frac{2016}{2017}:\frac{3}{5}\)

\(=\frac{3360}{2017}\)

Vậy B \(=\frac{3360}{2017}\)~~~~~

   (2/2017 + 2/2018) / (5/2017 + 5/2018)

= 2 x (1/2017 + 1/2018) / 5 x (1/2017 + 1/2018)

= 2/5 (vì (1/2017 + 1/2018) khác 0)

\(\frac{\frac{2}{2017}+\frac{2}{2018}}{\frac{5}{2017}+\frac{5}{2018}}\)

\(=\frac{2\left(\frac{1}{2017}+\frac{1}{2018}\right)}{5\left(\frac{1}{2017}+\frac{1}{2018}\right)}\)

\(=\frac{2}{5}\)

Study well ! >_<

\(\frac{\frac{2}{2017}+\frac{2}{2018}}{\frac{5}{2017}+\frac{5}{2018}}\)

\(=\frac{2\left(\frac{1}{2017}+\frac{1}{2018}\right)}{5\left(\frac{1}{2017}+\frac{1}{2018}\right)}\)

\(=\frac{2}{5}\)

Bạn làm theo cách này nhé:

\(\frac{7}{5}\div\frac{4}{5}=\frac{7}{4}\)(5 ở trên tử và 5 ở dưới mẫu triệt tiêu còn 1)

Ta có: \(\frac{7}{4}>1>\frac{2005}{2006}\Rightarrow\frac{7}{4}\div\frac{4}{5}>\frac{2005}{2006}\)

7/5:4/5=35/20 nhẩm ra =7/4.Mà 7/4>1,2005/2006<1neen 7/5:4/5>2005/2006  Mik nghi ko đến 4s đâu