\(\frac{3}{7}.\frac{9}{26}-\frac{1}{14}.\frac{1}{13}\)

\(=\frac{27}{182}-\frac{1}{182}\)

\(=\frac{1}{7}\)

\(\frac{3}{5}.\frac{13}{46}-\frac{1}{10}.\frac{16}{23}\)

\(=\frac{6}{10}.\frac{13}{46}-\frac{1}{10}.\frac{16}{23}\)

\(=\frac{1}{10}.\frac{78}{46}-\frac{1}{10}.\frac{16}{32}\)

\(=\frac{1}{10}\left(\frac{78}{46}-\frac{32}{46}\right)\)

\(=\frac{1}{10}.1=\frac{1}{10}\)

bằng 1/7 nha không tên

=27/182 - 1/182 

= 26/182 

= 1/7

bấm máy tính đi :D

= 27/182 - 1/182

= 26/182 

= 1/7

tổng của hai số lẻ liên tiếp là 636 . Tìm số bé hơn

Bài 1:

\(\frac{3}{7}\cdot\frac{9}{2}-\frac{1}{14}\cdot\frac{1}{13}\)=\(\frac{27}{14}-\frac{1}{14}\cdot\frac{1}{13}\)

                                          = \(\frac{1}{14}\left(27-\frac{1}{3}\right)\)

                                         = \(\frac{1}{14}\cdot\frac{350}{13}\)=\(\frac{25}{13}\)

bài 2:\(\frac{5}{9}\cdot\frac{7}{13}+\frac{5}{9}\cdot\frac{9}{13}\cdot\frac{3}{13}\)= \(\frac{5}{9}\cdot\frac{1}{13}\left(7+9\cdot\frac{3}{13}\right)\)

                                                            = \(\frac{5}{9}\cdot\frac{1}{13}\cdot\frac{94}{13}\)=\(\frac{470}{1521}\)

có j sai xin mn chỉ bảo!

=-3/7.(4/13+9/13)+3/7

=-3/7.13/13+3/7

=-3/7.1+3/7

=-3/7+3/7

=0

a) Ta có: \(\dfrac{3}{5\cdot7}+\dfrac{3}{7\cdot9}+...+\dfrac{3}{59\cdot61}\)

\(=\dfrac{3}{2}\left(\dfrac{2}{5\cdot7}+\dfrac{2}{7\cdot9}+...+\dfrac{2}{59\cdot61}\right)\)

\(=\dfrac{3}{2}\left(\dfrac{1}{5}-\dfrac{1}{61}\right)\)

\(=\dfrac{3}{2}\cdot\dfrac{56}{305}=\dfrac{84}{305}\)

a)

b) câu b, bạn vt hơi khó hiểu