`P = ( 1/(sqrta - 1) - 1/(sqrta) ) : ( (sqrta+1)/(sqrta-2) - (sqrta+2)/(sqrta-1) )` `( a > 0 ; a \ne 1 ; a \ne 4 )`

`= [ (sqrta)/(sqrta(sqrta-1)) - (sqrta-1)/(sqrta(sqrta-1)) ] :` `[ ((sqrta+1)(sqrta-1))/((sqrta-2)(sqrta-1)) - ((sqrta+2)(sqrta-2))/((sqrta-2)(sqrta-1))]`

`= (sqrta-sqrta+1)/(sqrta(sqrta-1)) : (a-1-a+4)/((sqrta-2)(sqrta-1))`

`= 1/(sqrta(sqrta-1)) . ((sqrta-2)(sqrta-1))/3`

`= (sqrta-2)/(3sqrta)`

Vậy `P = (sqrta-2)/(3sqrta)` với ` a > 0 ; a \ne 1 ; a \ne 4 `