Ta có: \(\frac{15}{14}\left(\frac{14}{9}-\frac{3}{7}\right)-\frac{15}{14}\left(\frac{14}{6}-\frac{3}{7}\right)\)

\(=\frac{15}{14}\left[\left(\frac{14}{9}-\frac{3}{7}\right)-\left(\frac{14}{6}-\frac{3}{7}\right)\right]\)

\(=\frac{15}{14}\left(\frac{14}{9}-\frac{3}{7}-\frac{14}{6}+\frac{3}{7}\right)\)

\(=\frac{15}{14}\left(\frac{14}{9}-\frac{14}{6}\right)\)

\(=\frac{15}{14}\cdot\left(\frac{28}{18}-\frac{42}{18}\right)\)

\(=\frac{15}{14}\cdot\frac{-14}{18}\)

\(=\frac{-15}{18}=-\frac{5}{6}\)

C

C

C

7 x 2 = 14       7 x 4 = 28       7 x 6 = 42       7 x 3 = 21

2 x 7 = 14       4 x 7 = 28       6 x 7 = 42       3 x 7 = 21

14 : 7 = 2       28 : 7 = 4       42 : 7 = 6       21 : 7 = 3

14 : 2 = 7       28 : 4 = 7       42 : 6 = 7       21 : 3 = 7

a)-112

b: =-30-15-21

=-66

95/21

14\(\dfrac{6}{7}\) : \(\left(\dfrac{4}{3}-\dfrac{5}{7}\right)\) + \(14\dfrac{6}{7}\) : \(\left(\dfrac{2}{3}-\dfrac{2}{7}\right)\)

= 14\(\dfrac{6}{7}\) : \(\dfrac{13}{21}\) + 14\(\dfrac{6}{7}\) : \(\dfrac{8}{21}\)

= 14\(\dfrac{6}{7}\) :\(\left(\dfrac{13}{21}+\dfrac{8}{21}\right)\)

= 14\(\dfrac{6}{7}\) : 1

= \(\dfrac{104}{7}\)

\(14\dfrac{6}{7}:\left(\dfrac{4}{3}-\dfrac{5}{7}\right)+14\dfrac{6}{7}:\left(\dfrac{2}{3}-\dfrac{2}{7}\right)\)

=\(14\dfrac{6}{7}:\left(\dfrac{13}{21}\right)+14\dfrac{6}{7}:\left(\dfrac{8}{21}\right)\)

=\(14\dfrac{6}{7}:\left(\dfrac{13}{21}+\dfrac{8}{21}\right)\)

=\(14\dfrac{6}{7}:1\)

=\(14\dfrac{6}{7}=\dfrac{104}{7}\)

C nha

C. 12/14

C mới đúng nhé

   2\(\dfrac{5}{7}\) + \(\dfrac{3}{14}\) - \(\dfrac{6}{7}\) + 0,5 + \(\dfrac{9}{14}\)

= 2 + \(\dfrac{5}{7}\) + (\(\dfrac{3}{14}\) + \(\dfrac{9}{14}\)) - \(\dfrac{6}{7}\) + 0,5

= ( 2 + \(\dfrac{1}{2}\)) + ( \(\dfrac{5}{7}\) - \(\dfrac{6}{7}\) ) + \(\dfrac{12}{14}\)

=   \(\dfrac{5}{2}\) - \(\dfrac{1}{7}\) + \(\dfrac{6}{7}\)

=  \(\dfrac{5}{2}\)+ \(\dfrac{5}{7}\)

=  \(\dfrac{35}{14}\) + \(\dfrac{10}{14}\)

= \(\dfrac{45}{14}\)

có đúng ko