Giải từng bước đúng nhất

` A = ( 4/(x -1 ) + (sqrtx + 3)/(sqrtx +1) + 5/(sqrtx - 1) ) : (sqrtx + 6)/sqrtx ` 

Điều kiện xác định  : 

` x > 0 ; x ne 1 ` 

` A = (  4/((sqrtx - 1)(sqrtx + 1)) + (sqrtx + 3)/(sqrtx + 1) + 5/(sqrtx -1) ) . (sqrtx )/(sqrtx +6) ` 

`A = ( 4/((sqrtx - 1)(sqrtx + 1)) + ((sqrtx + 3)(sqrtx -1 ))/((sqrtx - 1)(sqrtx + 1)) + (5(sqrtx + 1))/((sqrtx - 1)(sqrtx + 1)) ) . (sqrtx )/(sqrtx + 6) ` 

` A = ( 4/((sqrtx - 1)(sqrtx + 1)) + ( x - sqrtx + 3sqrtx -3)/((sqrtx - 1)(sqrtx + 1)) + (5sqrtx + 5)/((sqrtx - 1)(sqrtx + 1)) ) . ( sqrtx )/(sqrtx + 6) ` 

` A = ( 4/((sqrtx - 1)(sqrtx + 1)) + ( x + 2sqrtx - 3)/((sqrtx - 1)(sqrtx + 1)) + (5sqrtx + 5)/((sqrtx - 1)(sqrtx + 1)) ) . (sqrtx)/(sqrtx + 6) ` 

`A = ( 4 +  x + 2sqrtx - 3 + 5sqrtx + 5)/((sqrtx - 1)(sqrtx + 1)) .(sqrtx)/(sqrtx + 6) ` 

`A = ( x + 7sqrtx + 6)/((sqrtx - 1)(sqrtx + 1)) . (sqrtx )/(sqrtx + 6) ` 

`A = ( (sqrtx + 1)(sqrtx + 6))/((sqrtx - 1)(sqrtx + 1)) . (sqrtx)/(sqrtx + 6) ` 

`A = (sqrtx )/(sqrtx -1 ) ` 

Vậy ` A = (sqrtx)/(sqrtx - 1) ` với ` x > 0 ; x ne 1 `