`A = 2 1/315 . 1/651 - 1/105 . 3 650/651 - 4/{315.651} + 4/105`
`-> A = 631/315 . 1/651 - 1/105 . 2603/651 - 4/{315. 651} + 4/105`
`-> A = {631}/{315 . 651} - {2063}/{105 . 651} - 4/{315.651} + 4/105`
`-> A = (631/{315.651} - 4/{315.651} ) + ( {-2603}/{105 . 651} + 4/105 )`
`-> A = 627/{315 . 651} + ( {-2603}/{105.651} + {651 . 4}/ { 105 . 651} )`
`-> A = {627}/{315.651}+ ( {-2603}/{105.651} + {2604}/{105.651} )`
`-> A = 627/{315.651} + 1/{105.651}`
`-> A = {627 . 105}/{315.105 . 651} + {315}/{105.651.315}`
`-> A = {65835+315}/{315.105.651}`
`-> A = 2/651`
Vậy `A = 2/651`
