Đáp án:
$a)
\dfrac{-4}{35}\\
b) \dfrac{1}{12}\\
c) \dfrac{-5}{36}\\
d) \dfrac{-10}{21}\\
e)76\\
g) \dfrac{1}{9}\\
j)1$
Giải thích các bước giải:
$a)
\dfrac{-2}{5}+\dfrac{4}{14}\\
=\dfrac{-2}{5}+\dfrac{2}{7}\\
=\dfrac{(-2).7}{35}+\dfrac{2.5}{35}\\
=\dfrac{-4}{35}\\
b) \dfrac{7}{21}+\dfrac{9}{-36}\\
=\dfrac{1}{3}+\dfrac{-1}{4}\\
=\dfrac{4}{12}+\dfrac{-3}{12}\\
=\dfrac{1}{12}\\
c) \dfrac{-5}{9}-\dfrac{-5}{12}\\
=\dfrac{(-5).4}{36}-\dfrac{(-5).3}{36}\\
=\dfrac{-5}{36}\\
d) \dfrac{-5}{9}:1\dfrac{1}{6}\\
=\dfrac{-5}{9}:\dfrac{7}{6}\\
=\dfrac{-5}{9}.\dfrac{6}{7}\\
=\dfrac{-10}{21}\\
e)4.5^2-3.2^3\\
=4.25-3.8\\
=100-24=76\\
g) \dfrac{6}{7}+\dfrac{5}{7}:5-\dfrac{8}{9}\\
=\dfrac{6}{7}+\dfrac{5}{7}.\dfrac{1}{5}-\dfrac{8}{9}\\
=\dfrac{6}{7}+\dfrac{1}{7}-\dfrac{8}{9}\\
=1-\dfrac{8}{9}\\
=\dfrac{9}{9}-\dfrac{8}{9}=\dfrac{1}{9}\\
j) \dfrac{-3}{5}+\left ( 2+\dfrac{-2}{5} \right )\\
=\dfrac{-3}{5}+2+\dfrac{-2}{5}\\
=\left (\dfrac{-3}{5}+\dfrac{-2}{5} \right )+2\\
=-1+2=1$
