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MSC: 36
\(-\dfrac{7}{12}=-\dfrac{7\times3}{12\times3}=\dfrac{21}{36}\)
\(-\dfrac{11}{18}=-\dfrac{11\times2}{18\times2}=-\dfrac{22}{36}\)
\(\frac{11}{18}=\frac{11.9.12}{18.9.12}=\frac{1188}{1944}\)
\(\frac{-5}{9}=\frac{-5.18.12}{9.12.18}=\frac{-1080}{1944}\)
\(\frac{-7}{12}=\frac{-7.9.18}{12.9.18}=\frac{-1134}{1944}\)
\(\dfrac{5}{12}=\dfrac{5.3}{12.3}=\dfrac{15}{36};\dfrac{7}{18}=\dfrac{7.2}{18.2}=\dfrac{14}{36}\)
\(\dfrac{5}{12}\) = \(\dfrac{5.3}{12.3}\) = \(\dfrac{15}{36}\)
\(\dfrac{7}{18}\) = \(\dfrac{7.2}{18.2}\) = \(\dfrac{14}{36}\)
Vậy hai phân số \(\dfrac{5}{12}\) và \(\dfrac{7}{18}\) đã được quy đồng mẫu số lần lượt thành các phân số sau: \(\dfrac{15}{36}\); \(\dfrac{14}{36}\)
a) -12/18=-420/630
-21/35=-378/630
-420/630+378/630=-42/630=-1/15
b) 27/5=81/15
8/3 = 40/15
81/15+40/15=121/15
c) 11/4=77/28
9/7=36/28
77/28+36/28=113/28
a) -12/18=-420/630
-21/35=-378/630
-420/630+378/630=-42/630=-1/15
b) 27/5=81/15
8/3 = 40/15
81/15+40/15=121/15
c) 11/4=77/28
9/7=36/28
77/28+36/28=113/28
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: \(\dfrac{36}{42}=\dfrac{6}{7}=\dfrac{6\cdot3}{7\cdot3}=\dfrac{18}{21}\)
\(\dfrac{-12}{36}=\dfrac{-1}{3}=\dfrac{-1\cdot7}{3\cdot7}=\dfrac{-7}{21}\)
\(\dfrac{22}{36};-\dfrac{20}{36};-\dfrac{21}{36}\)