Lời giải:

a. $\frac{5}{9}=\frac{5\times 2}{9\times 2}=\frac{10}{18}$
b. $\frac{9}{20}=\frac{9\times 3}{20\times 3}=\frac{27}{60}$

a) \(\dfrac{5}{9}=\dfrac{5\times2}{9\times2}=\dfrac{10}{18}\)

b) \(\dfrac{9}{20}=\dfrac{9\times3}{20\times3}=\dfrac{27}{60}\)

a: \(\dfrac{5}{7}=\dfrac{5\cdot11}{7\cdot11}=\dfrac{55}{77}\)

\(\dfrac{9}{11}=\dfrac{9\cdot7}{11\cdot7}=\dfrac{63}{77}\)

b: \(\dfrac{36}{42}=\dfrac{6}{7}=\dfrac{6\cdot9}{7\cdot9}=\dfrac{54}{63}\)

\(-\dfrac{12}{54}=\dfrac{-2}{9}=\dfrac{-2\cdot7}{9\cdot7}=-\dfrac{14}{63}\)

c: \(\dfrac{-11}{30}=\dfrac{-11\cdot4}{30\cdot4}=\dfrac{-44}{120}\)

\(\dfrac{-17}{-40}=\dfrac{17}{40}=\dfrac{17\cdot3}{40\cdot3}=\dfrac{51}{120}\)

d: \(\dfrac{36}{42}=\dfrac{6}{7}=\dfrac{6\cdot3}{7\cdot3}=\dfrac{18}{21}\)

\(\dfrac{-12}{36}=\dfrac{-1}{3}=\dfrac{-1\cdot7}{3\cdot7}=\dfrac{-7}{21}\)

\(a,MSC:180\\ \dfrac{17}{12}=\dfrac{17.15}{12.15}=\dfrac{255}{180};\dfrac{31}{18}=\dfrac{31.10}{18.10}=\dfrac{310}{180};\dfrac{8}{15}=\dfrac{8.12}{15.12}=\dfrac{96}{180}\\ b,MSC:75\\ \dfrac{7}{15}=\dfrac{7.5}{15.5}=\dfrac{35}{75};\dfrac{8}{25}=\dfrac{8.3}{25.3}=\dfrac{24}{75};\dfrac{11}{75}=\dfrac{11}{75}\)

a)

MSC: 35

\(\dfrac{4}{7}=\dfrac{4\times5}{7\times5}=\dfrac{20}{35}\)

\(\dfrac{28}{35}\) giữ nguyên

b)

MSC: 100

\(\dfrac{13}{20}=\dfrac{13\times5}{20\times5}=\dfrac{65}{100}\)

c)

MSC: 24

\(\dfrac{5}{6}=\dfrac{5\times4}{6\times4}=\dfrac{20}{24}\)

\(\dfrac{9}{8}=\dfrac{9\times3}{8\times3}=\dfrac{27}{24}\)

a, 4/7 và 28/35

ta có :

4/7=20/35

28/35

b13/20 và 32/100

ta có :

13/20=65/100

32/100

c,5/6,9/8 và 11/24

ta có : 

5/6=20/24

9/8=27/24

11/24

a: 3/8=36/96

5/12=40/96

b: -2/9=-24/108

-5/12=-45/108

c: -3/16=-63/336

-5/24=-70/336

-21/56=-126/336

a)\(\dfrac{3}{7}=\dfrac{3.8}{7.8}=\dfrac{24}{56};\dfrac{5}{8}=\dfrac{5.7}{8.7}=\dfrac{35}{56}\)

b)\(\dfrac{7}{10}=\dfrac{7.2}{10.2}=\dfrac{14}{20};\dfrac{3}{20}\)

c)\(\dfrac{9}{20}=\dfrac{9.9}{20.9}=\dfrac{81}{180};\dfrac{2}{9}=\dfrac{2.20}{9.20}=\dfrac{40}{180}\)

ultr hôm nay học mà bn ko nhớ cách lm hẻ :))

a: 3/4=135/180

-1/9=-20/180

-5/5=-1=-180/180

a) \(\dfrac{3}{4}=\dfrac{3\cdot5}{4\cdot5}=\dfrac{15}{20}\\ \dfrac{2}{5}=\dfrac{2\cdot4}{5\cdot4}=\dfrac{8}{20}\)

b) \(\dfrac{5}{12}=\dfrac{5\cdot3}{12\cdot3}=\dfrac{15}{36}\\ \dfrac{11}{36}=\dfrac{11}{36}\)

c) \(\dfrac{2}{3}=\dfrac{2\cdot4\cdot5}{3\cdot4\cdot5}=\dfrac{40}{60}\\ \dfrac{3}{4}=\dfrac{3\cdot3\cdot5}{4\cdot3\cdot5}=\dfrac{45}{60}\\ \dfrac{4}{5}=\dfrac{4\cdot3\cdot4}{5\cdot3\cdot4}=\dfrac{48}{60}\)

a) \(\dfrac{3}{4}\) và \(\dfrac{2}{5}\)

Mẫu số chung: 20

\(\dfrac{3}{4}=\dfrac{3.5}{4.5}=\dfrac{15}{20}\)

\(\dfrac{2}{5}=\dfrac{2.4}{5.4}=\dfrac{8}{20}\)

b) \(\dfrac{5}{12}\) và \(\dfrac{11}{36}\)

Mẫu số chung: 36

\(\dfrac{5}{12}=\dfrac{5.3}{12.3}=\dfrac{15}{36}\)

c) \(\dfrac{2}{3};\dfrac{3}{4}\) và \(\dfrac{4}{5}\)

Mẫu số chung: 60

\(\dfrac{2}{3}=\dfrac{2.20}{3.20}=\dfrac{40}{60}\\ \dfrac{3}{4}=\dfrac{3.15}{4.15}=\dfrac{45}{60}\\ \dfrac{4}{5}=\dfrac{4.12}{5.12}=\dfrac{48}{60}\)

a) MTC=20

 \(\dfrac{3}{4}=\dfrac{15}{20}\)

\(\dfrac{2}{5}=\dfrac{8}{20}\)

b) MTC=36 

\(\dfrac{5}{12}=\dfrac{15}{36}\)

\(\dfrac{11}{36}=\dfrac{11}{36}\)

c) MTC=60

\(\dfrac{2}{3}=\dfrac{40}{60}\)

\(\dfrac{3}{4}=\dfrac{45}{60}\)

\(\dfrac{4}{5}=\dfrac{48}{60}\)

a) \(\dfrac{3}{5}=\dfrac{21}{35};\dfrac{4}{7}=\dfrac{20}{35}\)

b) \(\dfrac{5}{6}=\dfrac{45}{54};\dfrac{7}{9}=\dfrac{42}{54}\)