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\(a.-\dfrac{8}{12}=\dfrac{-2\cdot4}{4\cdot3}=-\dfrac{2}{3}\)
\(b.\dfrac{15}{-60}=\dfrac{15}{15\cdot-4}-\dfrac{1}{4}\)
\(c.\dfrac{-16}{-72}=\dfrac{-2\cdot8}{-9\cdot8}=\dfrac{2}{9}\)
\(d.\dfrac{35}{14\cdot15}=\dfrac{7\cdot5}{7\cdot2\cdot5\cdot3}=\dfrac{1}{6}\)
\(\dfrac{8}{12}\)=\(\dfrac{2}{31}\)
\(\dfrac{15}{-60}\)=\(\dfrac{-1}{4}\)
\(\dfrac{-16}{72}\)=\(\dfrac{-2}{9}\)
\(\dfrac{35}{14.15}=\dfrac{35}{210}=\dfrac{1}{6}\)
\(\dfrac{-63}{72}=\dfrac{-7}{8}\)
\(\dfrac{20}{-140}=\dfrac{-1}{7}\)
\(\dfrac{3.10}{5.24}=\dfrac{30}{120}=\dfrac{1}{4}\)
\(\dfrac{3.7.11}{22.9}=\dfrac{231}{198}=\dfrac{7}{6}\)
\(\dfrac{8.5-8.2}{16}=\dfrac{24}{16}=\dfrac{3}{2}\)
\(\dfrac{11.4-11}{2-13}=\dfrac{33}{-11}=-3\)
Ta có: \(-\frac{72}{45}=\frac{-72:9}{45:9}=\frac{-8}{5}\)
Câu 3:
a) \(\dfrac{12}{36}=\dfrac{12:12}{36:12}=\dfrac{1}{3}\)
\(\dfrac{-16}{20}=\dfrac{-16:4}{20:4}=\dfrac{-4}{5}\)
b) \(\dfrac{21}{105}=\dfrac{21:21}{105:21}=\dfrac{1}{5}\)
\(\dfrac{35}{150}=\dfrac{35:5}{150:5}=\dfrac{7}{30}\)
Câu 4:
a) \(\dfrac{3}{10}+\dfrac{5}{10}=\dfrac{3+5}{10}=\dfrac{8}{10}=\dfrac{4}{5}\)
b) Ta có: \(\left(-27\right)\cdot36+64\cdot\left(-27\right)+23\cdot\left(-100\right)\)
\(=\left(-27\right)\cdot\left(64+36\right)+23\cdot\left(-100\right)\)
\(=-27\cdot100-23\cdot100\)
\(=100\left(-27-23\right)\)
\(=-50\cdot100=-5000\)
c) \(\dfrac{5}{8}+\dfrac{3}{12}=\dfrac{15}{24}+\dfrac{6}{24}=\dfrac{21}{24}=\dfrac{7}{8}\)
d) Ta có: \(\dfrac{-2}{17}+\dfrac{3}{19}+\dfrac{-15}{17}+\dfrac{16}{19}+\dfrac{5}{6}\)
\(=\left(-\dfrac{2}{17}+\dfrac{-15}{17}\right)+\left(\dfrac{3}{19}+\dfrac{16}{19}\right)+\dfrac{5}{6}\)
\(=-1+1+\dfrac{5}{6}\)
\(=\dfrac{5}{6}\)