cấp mấy đấy

a: \(=\dfrac{17}{19}\cdot\dfrac{19}{17}\cdot\dfrac{4}{5}=\dfrac{4}{5}\)

b: \(=\dfrac{14}{7}\cdot\dfrac{7}{6}=2\cdot\dfrac{7}{6}=\dfrac{14}{6}=\dfrac{7}{3}\)

c: =13/14(4/5+1/5)=13/14

\(\dfrac{17}{19}\times\dfrac{12}{15}\times\dfrac{19}{17}=\dfrac{12}{15}\)

\(\left(\dfrac{5}{7}+\dfrac{9}{7}\right)\times\dfrac{21}{18}=2\times\dfrac{7}{6}=\dfrac{7}{3}\)

\(\dfrac{4}{5}\times\dfrac{13}{14}+\dfrac{13}{14}\times\dfrac{1}{5}=\dfrac{13}{14}\)

\(\dfrac{17}{19}\times\dfrac{12}{15}\times\dfrac{19}{17}.\\ =\dfrac{17}{19}\times\dfrac{19}{17}\times\dfrac{12}{15}.\\ =1\times\dfrac{12}{15}=\dfrac{12}{15}.\\ \left(\dfrac{5}{7}+\dfrac{9}{7}\right)\times\dfrac{21}{18}.\\ =2\times\dfrac{7}{6}=\dfrac{7}{3}.\\ \dfrac{4}{5}\times\dfrac{13}{14}+\dfrac{13}{14}\times\dfrac{1}{5}.\\ =\left(\dfrac{4}{5}+\dfrac{1}{5}\right)\times\dfrac{13}{14}.\\ =1\times\dfrac{13}{14}.\\ =\dfrac{13}{14}.\)

Cách hai:

A; \(\dfrac{17}{19}\) x \(\dfrac{12}{15}\) x \(\dfrac{19}{17}\)

= \(\dfrac{68}{95}\) x \(\dfrac{19}{17}\)

= \(\dfrac{4}{5}\)

Cách 1:

A. \(\dfrac{17}{19}\) x \(\dfrac{12}{15}\) x \(\dfrac{19}{17}\)

= (\(\dfrac{17}{19}\) x \(\dfrac{19}{17}\)) x \(\dfrac{12}{15}\)

= \(1\) x \(\dfrac{12}{15}\)

= \(\dfrac{4}{5}\)

B; Cách 1: (\(\dfrac{5}{7}\) + \(\dfrac{9}{7}\)) x \(\dfrac{21}{28}\)

                 =  2 x \(\dfrac{3}{4}\)

                 =   \(\dfrac{3}{2}\)

Cách 2:   (\(\dfrac{5}{7}+\dfrac{9}{7}\)) x \(\dfrac{21}{28}\) 

             =  \(\dfrac{5}{7}\) x \(\dfrac{21}{28}\) + \(\dfrac{9}{7}\) x \(\dfrac{21}{28}\)

             =   \(\dfrac{15}{28}\) + \(\dfrac{27}{28}\)

            = \(\dfrac{42}{28}\)

            = \(\dfrac{3}{2}\)

 câu A cách 1 

 \(\dfrac{17}{19}\times\dfrac{12}{15}\times\dfrac{19}{17}\) 

=\(\dfrac{17\times12\times19}{19\times15\times17}\) 

=\(\dfrac{12}{15}\)

câu A cách 2 

\(\dfrac{17}{19}\times\dfrac{12}{15}\times\dfrac{19}{17}\) 

=\(\dfrac{17}{19}\times\dfrac{19}{17}\times\dfrac{12}{15}\) 

=1 x \(\dfrac{12}{15}\) 

=\(\dfrac{12}{15}\)

a: =35/17-18/17-9/5+4/5

=1-1=0

b: =-7/19(3/17+8/11-1)

=7/19*18/187=126/3553

c: =26/15-11/15-17/3-6/13

=1-6/13-17/3

=7/13-17/3=-200/39