Đáp án:
$1)
a)
0\\
b) \dfrac{7}{12}\\
c)
1\\
d)
\dfrac{11}{5}\\
2)
a)
x=2\\
b)x=76.(-15)=-1140\\
c)
x=\dfrac{-105}{11}$
Giải thích các bước giải:
$1)
a)
2020+(-2021)+2019^0=2020-2021+1=2020-2020=0\\
b) \dfrac{-3}{4}:\dfrac{5}{13}+\dfrac{-3}{4}:\dfrac{5}{2}+2\dfrac{5}{6}\\
=\dfrac{-3}{4}.\dfrac{13}{5}+\dfrac{-3}{4}.\dfrac{2}{5}+\dfrac{17}{6}\\
=\dfrac{-3}{4}.\left ( \dfrac{13}{5}+\dfrac{2}{5} \right )+\dfrac{17}{6}\\
=\dfrac{-3}{4}.\dfrac{15}{5}+\dfrac{17}{6}\\
=\dfrac{-9}{4}+\dfrac{17}{6}\\
=\dfrac{(-9).3}{12}+\dfrac{17.2}{12}\\
=\dfrac{-27+34}{12}\\
=\dfrac{7}{12}\\
c)
\dfrac{6}{11}+\dfrac{5}{11}.\dfrac{1105}{2016}+\dfrac{5}{11}.\dfrac{911}{2016}\\
=\dfrac{6}{11}+\dfrac{5}{11}.\left (\dfrac{1105}{2016}+\dfrac{911}{2016} \right )\\
=\dfrac{6}{11}+\dfrac{5}{11}.\dfrac{1105+911}{2016}\\
=\dfrac{6}{11}+\dfrac{5}{11}.\dfrac{2016}{2016}\\
=\dfrac{6}{11}+\dfrac{5}{11}\\
=\dfrac{11}{11}=1\\
d)
\dfrac{75}{100}-1\dfrac{1}{2}+0,5:\dfrac{5}{12}-\left ( -\dfrac{1}{2} \right )^2\\
=\dfrac{3}{4}-\dfrac{3}{2}+\dfrac{1}{2}.\dfrac{12}{5}-\dfrac{1}{4}\\
=\left (\dfrac{3}{4}-\dfrac{1}{4} \right )-\dfrac{3}{2}+\dfrac{6}{5}\\
=\dfrac{2}{4}-\dfrac{3}{2}+\dfrac{6}{5}\\
=\dfrac{1}{2}-\dfrac{3}{2}+\dfrac{6}{5}\\
=\dfrac{-2}{2}+\dfrac{6}{5}\\
=1+\dfrac{6}{5}\\
=\dfrac{5}{5}+\dfrac{6}{5}\\
=\dfrac{11}{5}\\
2)
a)
\dfrac{x}{7}=\dfrac{6}{21}\\
\Leftrightarrow x=\dfrac{6.7}{7.3}=2\\
b)\dfrac{60}{100}.x-\dfrac{2}{3}x=76\\
\Leftrightarrow \left (\dfrac{3}{5}-\dfrac{2}{3} \right )x=76\\
\Leftrightarrow \left (\dfrac{9}{15}-\dfrac{10}{15} \right )x=76\\
\Leftrightarrow \dfrac{-1}{15}x=76\\
\Leftrightarrow x=76.(-15)=-1140\\
c)
\dfrac{4}{9}+\dfrac{7}{3}:x=\dfrac{1}{5}\\
\Leftrightarrow \dfrac{7}{3}.\dfrac{1}{x}=\dfrac{1}{5}-\dfrac{4}{9}\\
\Leftrightarrow \dfrac{7}{3}.\dfrac{1}{x}=\dfrac{9}{45}-\dfrac{20}{45}\\
\Leftrightarrow \dfrac{7}{3}.\dfrac{1}{x}=\dfrac{-11}{45}\\
\Leftrightarrow \dfrac{1}{x}=\dfrac{-11}{45}.\dfrac{3}{7}\\
\Leftrightarrow \dfrac{1}{x}=\dfrac{-11}{105}\\
\Leftrightarrow x=\dfrac{-105}{11}$
