`A = ( 1/2^2 - 1 ) . ( 1/3^2 - 1 ) . ( 1/4^2 - 1 ) .... ( 1/2014^2 - 1 )`
`A = ( 1/4 - 1 ) . ( 1/9 - 1 ) . ( 1/16 - 1 ) .... ( 1/4056196 - 1 )`
`A = ( - 3 )/4 . ( - 8 )/9 . ( - 15 )/16 .... ( - 4056195 )/4056196`
`A = ( ( - 3 ) . ( - 8 ) . ( - 15 ) .... ( - 4056195 ) )/( 4 . 9 . 16 .... 405616 )`
`A = ( ( - 1 ) . 3 . ( - 2 ) . 4 . ( - 3 ) . 5 .... ( - 2013 ) . 2015 )/( ( 2 . 2 ) . ( 3 . 3 ) . ( 4 . 4 ) .... ( 2014 . 2014 ) )`
`A = ( [ ( - 1 ) . ( - 2 ) . ( - 3 ) .... ( - 2013 ) ] . [ 3 . 4 . 5 .... 2015 ] )/( ( 2 . 3 . 4 .... 2014 ) . ( 2 . 3 . 4 .... 2014 ) )`
`A = ( ( - 1 ) . 2015 )/( 2014 . 2 )`
`A = ( - 2015 )/4028`
Vì `A = ( - 2015 )/4028 < ( - 2014 )/4028` mà `( - 2014 )/4028 = ( - 1 )/2 = B`
`⇒ A < B`
Vậy `, A < B .`
