Đáp án:
$2)
a) \dfrac{271}{105}\\
b) \dfrac{-199}{36}\\
2)
a)\dfrac{5}{2}\\
b) \dfrac{30}{11}\\
c) \dfrac{-7}{2}\\
d) \dfrac{-3}{10}\\
4)
a) 5,5\\
b)0,4\\
c) \dfrac{-1}{3}\\
d) \dfrac{-1}{3}\\
5) a)x=\dfrac{5}{12}\\
b) x=\dfrac{39}{35}\\
c) x=\dfrac{4}{21}\\
6)
A=\dfrac{-5}{2}$
Giải thích các bước giải:
$2)
a) \dfrac{5}{3}+\left ( \dfrac{-2}{7} \right )-(-1,2)\\
=\dfrac{5}{3}-\dfrac{2}{7}+\dfrac{12}{10}\\
=\dfrac{5}{3}-\dfrac{2}{7}+\dfrac{6}{5}\\
=\dfrac{175}{105}-\dfrac{30}{105}+\dfrac{126}{105}\\
=\dfrac{271}{105}\\
b) \dfrac{-4}{9}+\left (\dfrac{-5}{6} \right )-\dfrac{17}{4}\\
=\dfrac{-16}{36}+\left (\dfrac{-30}{36} \right )-\dfrac{153}{36}\\
=\dfrac{-199}{36}\\
2)
5\dfrac{1}{2}+(-3)=\dfrac{11}{2}-3\\
=\dfrac{11}{2}-\dfrac{6}{2}\\
=\dfrac{5}{2}\\
b) 4\dfrac{9}{11}+\left ( -2\dfrac{1}{11} \right )\\
=\dfrac{53}{11}-\dfrac{23}{11}\\
=\dfrac{30}{11}\\
c) 2\dfrac{1}{2}+(-6)\\
=\dfrac{5}{2}-\dfrac{12}{2}\\
=\dfrac{-7}{2}\\
d) \left ( \dfrac{-4}{5} \right )+\dfrac{1}{2}\\
=\dfrac{-8}{10}+\dfrac{5}{10}\\
=\dfrac{-3}{10}\\
4)
a) 4,3-(-1,2)=4,3+1,2=5,5\\
b)0-(-0,4)=0,4\\
c) \dfrac{-2}{3}-\dfrac{-1}{3}=\dfrac{-2}{3}+\dfrac{1}{3}=\dfrac{-1}{3}\\
d) \dfrac{-1}{2}-\dfrac{-1}{6}\\
=\dfrac{-3}{6}+\dfrac{1}{6}\\
=\dfrac{-2}{6}=\dfrac{-1}{3}\\
5) a)x+\dfrac{1}{3}=\dfrac{3}{4}\\
\Leftrightarrow x=\dfrac{3}{4}-\dfrac{1}{3}\\
\Leftrightarrow x=\dfrac{9}{12}-\dfrac{4}{12}\\
\Leftrightarrow x=\dfrac{5}{12}\\
b) x-\dfrac{2}{5}=\dfrac{5}{7}\\
\Leftrightarrow x=\dfrac{5}{7}+\dfrac{2}{5}\\
\Leftrightarrow x=\dfrac{25}{35}+\dfrac{14}{35}\\
\Leftrightarrow x=\dfrac{39}{35}\\
c)-x-\dfrac{2}{3}=\dfrac{-6}{7}\\
\Leftrightarrow x=\dfrac{-2}{3}+\dfrac{6}{7}\\
\Leftrightarrow x=\dfrac{-14}{21}+\dfrac{18}{21}\\
\Leftrightarrow x=\dfrac{4}{21}\\
6)
A=\left ( 6-\dfrac{2}{3}+\dfrac{1}{2} \right )-\left ( 5+\dfrac{5}{3}-\dfrac{3}{2} \right )-\left ( 3-\dfrac{7}{3}+\dfrac{5}{2} \right )\\
=6-\dfrac{2}{3}+\dfrac{1}{2} -5-\dfrac{5}{3}+\dfrac{3}{2} - 3+\dfrac{7}{3}-\dfrac{5}{2} \\
=(6-5-3)+\left ( \dfrac{-2}{3}-\dfrac{5}{3}+\dfrac{7}{3} \right )+\left ( \dfrac{1}{2}+\dfrac{3}{2}-\dfrac{5}{2} \right )\\
=-2+0-\dfrac{1}{2}\\
=\dfrac{-4}{2}-\dfrac{1}{2}\\
=\dfrac{-5}{2}$
