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\(\dfrac{-8}{12}=\dfrac{-8:4}{12:4}=\dfrac{-2}{3}\\ \dfrac{15}{-60}=\dfrac{15:15}{-60:15}=\dfrac{1}{-4}\\ \dfrac{-16}{-72}=\dfrac{-16:\left(-8\right)}{-72:\left(-8\right)}=\dfrac{2}{9}\\ \dfrac{35}{14.15}=\dfrac{5.7}{7.2.5.3}=\dfrac{1}{2.3}=\dfrac{1}{6}\)
-8/12 rút gọn bằng-2/3; 15/-60 =-1/4; -16/-72=2/9;35/14.15=1/6
\(\frac{-8}{12}=\frac{-2}{3}\)
\(\frac{15}{-60}=\frac{-1}{4}\)
\(\frac{-16}{-72}=\frac{2}{9}\)
\(\frac{35}{14.15}=\frac{1}{6}\)
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: \(\dfrac{-2}{17}+\dfrac{3}{19}+\dfrac{-15}{17}+\dfrac{16}{19}+\dfrac{5}{6}\)
\(=\left(-\dfrac{2}{17}+\dfrac{-15}{17}\right)+\left(\dfrac{3}{19}+\dfrac{16}{19}\right)+\dfrac{5}{6}\)
\(=-1+1+\dfrac{5}{6}\)
\(=\dfrac{5}{6}\)
\(a.-\dfrac{8}{12}=\dfrac{-2\cdot4}{4\cdot3}=-\dfrac{2}{3}\)
\(b.\dfrac{15}{-60}=\dfrac{15}{15\cdot-4}-\dfrac{1}{4}\)
\(c.\dfrac{-16}{-72}=\dfrac{-2\cdot8}{-9\cdot8}=\dfrac{2}{9}\)
\(d.\dfrac{35}{14\cdot15}=\dfrac{7\cdot5}{7\cdot2\cdot5\cdot3}=\dfrac{1}{6}\)
\(\dfrac{8}{12}\)=\(\dfrac{2}{31}\)
\(\dfrac{15}{-60}\)=\(\dfrac{-1}{4}\)
\(\dfrac{-16}{72}\)=\(\dfrac{-2}{9}\)
\(\dfrac{35}{14.15}=\dfrac{35}{210}=\dfrac{1}{6}\)