Rút gọn biểu thức : `A` = ( $\frac{3}{x+3}$ - $\frac{9}{x^2+6x+9}$ ) : ( $\frac{3}{x^2-9}$ - $\frac{1}{3-x}$ )

Đáp án:

$\texttt{d.a.r.i}$

`A = (3/[x + 3] - 9/[x^2 + 6x + 9]) : (3/[x^2 - 9] - 1/[3 - x])` `(x \ne +- 3)`

`A = ([3.(x + 3)]/[(x + 3)^2] - 9/[(x + 3)^2]) : (3/[(x - 3).(x + 3)] + 1/[x - 3])`

`A = ([3x + 9]/[(x + 3)^2] - 9/[(x + 3)^2]) : (3/[(x - 3).(x + 3)] + [x + 3]/[(x - 3).(x + 3)] )`

`A = [3x + 9 - 9]/[(x + 3)^2] : [3 + x + 3]/[(x - 3).(x + 3)]`

`A = [3x]/[(x + 3)^2] : [x + 6]/[(x - 3).(x + 3)]`

`A = [3x]/[(x + 3)^2] . [(x - 3).(x + 3)]/[x + 6]`

`A = [3x.(x - 3).(x + 3)]/[(x + 3)^2.(x + 6)]`

`A = [3x.(x - 3)]/[(x + 3).(x + 6)]`