Đáp án:
$3)
a)\dfrac{-13}{3}\\
b)
\dfrac{-107}{18}\\
c)
\dfrac{8}{9}\\
d)
\dfrac{3}{4}$
Giải thích các bước giải:
$3)
a)\dfrac{3}{4}-\left ( 2\dfrac{1}{3}+\dfrac{3}{4} \right )+2^2.\left ( -\dfrac{1}{2} \right )\\
=\dfrac{3}{4}-2\dfrac{1}{3}-\dfrac{3}{4}+4.\dfrac{-1}{2}\\
=\dfrac{-7}{3}-2\\
=\dfrac{-7}{3}-\dfrac{6}{3}\\
=\dfrac{-13}{3}\\
b)
-4\dfrac{5}{6}+\dfrac{1}{6}.\left ( 5\dfrac{1}{3}-12 \right )\\
=\dfrac{-29}{6}+\dfrac{1}{6}.\left ( \dfrac{16}{3}-12 \right )\\
=\dfrac{-29}{6}+\dfrac{1}{6}. \dfrac{16}{3}-2 \\
=\dfrac{-29}{6}+\dfrac{8}{9}-2\\
=\dfrac{(-29).3}{18}+\dfrac{8.2}{18}-\dfrac{2.18}{18}\\
=\dfrac{-107}{18}\\
c)
\dfrac{2}{3}+\dfrac{1}{3}.\left ( -\dfrac{4.2}{18}+\dfrac{5.3}{18} \right ).\dfrac{12}{7}\\
=\dfrac{2}{3}+\dfrac{1}{3}.\dfrac{7}{18}.\dfrac{12}{7}\\
=\dfrac{2}{3}+\dfrac{2}{9}\\
=\dfrac{6}{9}+\dfrac{2}{9}\\
=\dfrac{8}{9}\\
d)
\left ( \dfrac{3}{8}+\dfrac{-3}{4}+\dfrac{7}{12}\right ):\dfrac{5}{6}+\dfrac{1}{2}\\
=\left ( \dfrac{9}{24}+\dfrac{-18}{24}+\dfrac{14}{24}\right ).\dfrac{6}{5}+\dfrac{1}{2}\\
=\dfrac{5}{24}.\dfrac{6}{5}+\dfrac{1}{2}\\
=\dfrac{1}{4}+\dfrac{1}{2}\\
=\dfrac{1}{4}+\dfrac{2}{4}\\
=\dfrac{3}{4}$
