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

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

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

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

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

ko hiểu

ko hiểu thì thôi

13212

\(\dfrac{5}{12}+1\dfrac{5}{7}+\dfrac{7}{2}-\dfrac{5}{7}-\dfrac{19}{14}\)

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

\(=\dfrac{7}{2}\)

a) 12 + 3 = 15     15 + 4 = 19     8 + 2 = 10     14 + 3 = 17

15 - 3 = 12     19 - 4 = 15     10 - 2 = 8     17 - 3 = 14

b) 11 + 4 + 2 = 17     19 - 5 - 4 = 10     14 + 2 - 5 = 11

\(\frac{-5}{19}\cdot\frac{8}{19}+\frac{-14}{19}\cdot\frac{8}{19}-\frac{11}{19}\)

\(=\frac{8}{19}\left(\frac{-5}{19}+\frac{-14}{19}\right)-\frac{11}{19}\)

\(=\frac{8}{19}\cdot\left(-1\right)-\frac{11}{19}\)

\(=\frac{-8}{19}-\frac{11}{19}\)

\(=-1\)

=))

fggfggfgfg

^fgfgfgfg

- Viết phép tính sao cho các số cùng hàng thẳng cột với nhau.

- Tính trừ lần lượt từ phải sang trái.