Question

Answer 1

1: Để 2n/n-2 là số nguyên thì 2n-4+4 chia hết cho n-2

\(\Leftrightarrow n-2\in\left\{1;-1;2;-2;4;-4\right\}\)

hay \(n\in\left\{3;1;4;0;6;-2\right\}\)

2: \(=\dfrac{3}{2}\left(\dfrac{2}{10\cdot12}+\dfrac{2}{12\cdot14}+...+\dfrac{2}{48\cdot50}\right)\)

\(=\dfrac{3}{2}\left(\dfrac{1}{10}-\dfrac{1}{12}+...+\dfrac{1}{48}-\dfrac{1}{50}\right)\)

\(=\dfrac{3}{2}\cdot\dfrac{2}{25}=\dfrac{3}{25}\)