Question

Answer 1

a)
\(=\dfrac{1}{4}\left(\dfrac{2}{5}+\dfrac{3}{5}\right)=\dfrac{1}{4}.1=\dfrac{1}{4}\)
b)
\(=\dfrac{-5}{3}\left(\dfrac{2}{13}+\dfrac{11}{13}\right)=\dfrac{-5}{3}.1=\dfrac{-5}{3}\)
c)
\(=\dfrac{4}{25}+\dfrac{21}{25}.1-\dfrac{5}{24}:\dfrac{7}{12}\)
\(=\dfrac{4}{25}+\dfrac{21}{25}-\dfrac{5}{14}=1-\dfrac{5}{14}=\dfrac{9}{14}\)

Answer 2

4: Để A nguyên thì \(5n-1\in\left\{1;-1;3;-3;9;-9\right\}\)

\(\Leftrightarrow5n\in\left\{0;10\right\}\)

hay \(n\in\left\{0;2\right\}\)