Tính bằng cách thuận tiện a,12 x 17 x21/ 63 x 51 x 9 b, 20082008 x 2012 / 20122012x 2010

`a, (12 .17 . 21)/ (63 . 51 . 9)`

`= (2.2. 3 .17 . 3.7)/ (3.3.7 . 3.17 . 3.3)`

`= 4/27`

`b, (20082008 . 2012) / (20122012 . 2010)`

`= (2.1004.10001 . 2012) / (2012.10001 . 2.1005)`

`= 1004/1005`

` a, (12.17.21)/(63.51.9)`

`= ( 3.3.4.7.17)/(3.3.3.3.7.3.17)`

`= 4/27`

`b, (20082008 . 2012)/(20122012.2010)`

`= (10001.2008.2012)/(2012.10001.2010)`

`= 2008/2010`

`=1004/1005`