bài 1
a) `-3/4`+`3/7`+`-1/4` +`4/9`+`4/7`
= ( `-3/4 + `-1/4`) +( `3/7`+`4/7`)
= `-4/4` + `7/7`
= (-1) + 1
0
b) `-7/9` . `4/11` + `-7/9`.`7/11` + 5`7/9`
= `-7/9` . ( `4/11`+`7/11`) + 52/9
= `-7/9` . `11/11` + `52/9`
= `-7/9`. 1 + `52/9`
= `-7/9` + `52/9`
= `45/9`
= 5
c)(`21/31`+ `2013/6039`) - (`44/53` - `10/31`) - `9/53`
= `21/31`+ `2013/6039` -`44/53` +`10/31` -`9/53`
= (`21/31`+`10/31` ) -(`44/53`+`9/53`) + `2013/6039`
= `31/31` - 53/53 + `2013/6039`
= 1 - 1 + `2013/6039`
= 0 + `2013/6039`
= `2013/6039`
= `1/3`
