Ta có : \(1\cdot3\cdot5\cdot...\cdot99=\frac{1\cdot2\cdot3\cdot4\cdot...\cdot99\cdot100}{2\cdot4\cdot6\cdot...\cdot100}\)
\(=\frac{1}{2\cdot1}\cdot\frac{2}{2\cdot2}\cdot...\cdot\frac{100}{2\cdot50}=\frac{1\cdot2\cdot3\cdot4\cdot...\cdot100}{1\cdot2\cdot3\cdot...\cdot50\cdot2\cdot2\cdot2\cdot...\cdot2}\)( 50 thừa số 2 )
\(=\frac{51\cdot51\cdot...\cdot100}{2\cdot2\cdot2\cdot...\cdot2}\)\(=\frac{51}{2}\cdot\frac{52}{2}\cdot\frac{53}{2}\cdot...\cdot\frac{100}{2}\)
Vậy A = B
Chúc bn hok tốt !!! ^_^