Ta rút gọn:

\(\frac{12}{15}=\frac{4}{5}=\frac{48}{60}\)

\(\frac{14}{-21}=\frac{-2}{3}=\frac{-40}{60}\)

\(\frac{-21}{-18}=\frac{21}{18}=\frac{7}{6}=\frac{70}{60}\)

a/ \(\frac{5}{6n}\)và \(\frac{7}{15}\)

=> MSC = \(6n\cdot15=90n\)

\(\Rightarrow\frac{5}{6n}=\frac{5\cdot15}{90n}=\frac{75}{90n}\)

\(\Rightarrow\frac{7}{15}=\frac{7\cdot6n}{90n}=\frac{42n}{90n}\)

b/  \(\frac{9x}{24}\)và \(\frac{12}{36}\)

=> MSC = 72

\(\Rightarrow\frac{9x}{24}=\frac{9x\cdot3}{72}=\frac{27x}{72}\)

\(\Rightarrow\frac{12}{36}=\frac{12\cdot2}{72}=\frac{24}{72}\)

a)MSC = 6n . 15 = 90n

5/6n = 5 . 15/60n . 15 = 75/90n

7/15 = 7 . 6n/15 . 6n =42n/90n

            #Louis

\(\frac{9}{12}=\frac{45}{60};\frac{7}{15}=\frac{28}{60}\)

\(\frac{7}{10}=\frac{98}{140};\frac{3}{4}=\frac{105}{140};\frac{9}{14}=\frac{90}{140}\)

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a\(\frac{27}{36}va\frac{21}{45}\)

a)\(\dfrac{11}{120};\dfrac{21}{120}\)

b)\(\dfrac{312}{1898};\dfrac{876}{1898}\)

c)\(\dfrac{28}{120};\dfrac{26}{120};\dfrac{-27}{120}\)

d)\(\dfrac{51}{180};\dfrac{-50}{180};\dfrac{-128}{180}\)

\(\frac{12}{47}>\frac{12}{48}=\frac{1}{4}\)

\(\frac{19}{77}< \frac{19}{76}=\frac{1}{4}\)

\(\Rightarrow\frac{12}{47}>\frac{19}{77}\)

\(\frac{58}{89}< \frac{58}{87}=\frac{2}{3}\)

\(\frac{36}{53}>\frac{36}{54}=\frac{2}{3}\)

\(\Rightarrow\frac{58}{89}< \frac{36}{53}\)

\(\frac{5}{14}=\frac{5.20}{14.20}=\frac{100}{280}\)

\(\frac{3}{-40}=\frac{3.\left(-7\right)}{\left(-40\right).\left(-7\right)}=\frac{-21}{280}\)

\(\frac{-13}{-140}=\frac{13}{140}=\frac{13.2}{140.2}=\frac{26}{280}\)