\(A=1\cdot2\cdot3\cdot...\cdot100\cdot\left(\left(1+\frac{1}{100}\right)+\left(\frac{1}{2}+\frac{1}{99}\right)+\left(\frac{1}{3}+\frac{1}{98}\right)+...+\left(\frac{1}{50}+\frac{1}{51}\right)\right)\) \(=1\cdot2\cdot3\cdot...\cdot100\cdot\left(\frac{101}{100}+\frac{101}{2\cdot99}+\frac{101}{3\cdot98}+...+\frac{101}{50\cdot51}\right)\)
\(=1\cdot2\cdot3\cdot...\cdot100\cdot101\cdot\left(\frac{1}{100}+\frac{1}{2\cdot99}+\frac{1}{3\cdot98}+...+\frac{1}{50\cdot51}\right)\)
vì \(101⋮101\Rightarrow A⋮101\)
A=1⋅2⋅3⋅...⋅100⋅((1+1100)+(12+199)+(13+198)+...+(150+151))A=1⋅2⋅3⋅...⋅100⋅((1+1100)+(12+199)+(13+198)+...+(150+151)) =1⋅2⋅3⋅...⋅100⋅(101100+1012⋅99+1013⋅98+...+10150⋅51)=1⋅2⋅3⋅...⋅100⋅(101100+1012⋅99+1013⋅98+...+10150⋅51)
=1⋅2⋅3⋅...⋅100⋅101⋅(1100+12⋅99+13⋅98+...+150⋅51)=1⋅2⋅3⋅...⋅100⋅101⋅(1100+12⋅99+13⋅98+...+150⋅51)
vì 101⋮101⇒A⋮101
