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b) = 27.(58+42)
= 27.100=2700
d) =18.(68+39-7)
=18.100=1800
a, UCLN(42;58) = 2
b, UCLN(18;30;42) = 6
c, UCLN(26;39;48) = 1
d, UCLN(85;161) = 1
\(\frac{6}{18}+\frac{-14}{21}=\frac{1}{3}+\frac{-2}{3}=\frac{-1}{3}\); ;
\(\frac{6}{13}+\frac{-14}{39}=\frac{18}{39}+\frac{-14}{39}=\frac{4}{39}\);
\(\frac{-3}{21}+\frac{6}{42}=\frac{-1}{7}+\frac{1}{7}=0\);
\(\frac{7}{21}+\frac{9}{-36}=\frac{1}{3}+\frac{-1}{4}=\frac{4}{12}+\frac{-3}{12}=\frac{1}{12}\)
\(a,=57\left(158-57\right)+38=57\cdot101+38=5719\)
b, Đề sai
\(-\dfrac{18}{42}\cdot\dfrac{35}{42}:\dfrac{-98}{42}\)
\(=-\dfrac{18}{42}\cdot\dfrac{35}{42}\cdot\dfrac{42}{-98}\)
\(=\dfrac{-18}{42}\cdot\dfrac{-5}{14}\\ =\dfrac{15}{98}\)
\(\dfrac{-18}{42}.\dfrac{3\text{5}}{42}:\dfrac{-98}{42}\)
\(=\dfrac{-18}{42}.\dfrac{3\text{5}}{42}.\dfrac{-42}{98}\)
\(=\dfrac{1\text{5}}{98}\)
\(\left(39\times42-37\times42\right):42\)
\(=\left[42\left(39-37\right)\right]:42\)
\(=42.2:42=84:42\)
\(=2\)