Gấpppppppppppppppppp

Ta có:

`2/3 < 3/4`

`4/5 < 5/6`

`6/7 < 7/8`

`...`

`5000/5001 < 5001/5002`

`=> B = 3/4*5/6*7/8*...*5001/5002 > A`

`=> A*A < A*B`

Mà `A*B=(2/3*4/5*6/7*...*5000/5001)*(3/4*5/6*7/8*...*5001/5002)`

`= 2/3*3/4*4/5*5/6*...*5000/5001*5001/5002`

`=(2*3*4*5*...*5001)/(3*4*5*6*...*5002`

`=2/5002 = 1/2501`

Mà `1/2501 < 1/2500`

`1/2500 = (1/50)^2 (= 0,02)`

`=> A<0,02`

`---`

@ngnlnh