Đáp án:
a) $ A = 2x - \sqrt{x^2 + 4x +4}$
$\Rightarrow 2x -\sqrt{x^2 + 4x +2^2} $
$\Rightarrow 2x -\sqrt{(x+2)^2} $
$\Rightarrow 2x -| x + 2| $
b)$\Rightarrow 2x - | x +2| =-10$
$\Rightarrow |x +2| =2x + 10 $
$\Rightarrow \left[\begin{matrix} |x+2| = x+ 2 => x + 2 \ge 0 => x \ge -2\\ |x + 2| =-x - 2 => x + 2 < 0 => x < -2\end{matrix}\right.$
$\Rightarrow \left[\begin{matrix} x +2 = 2x +10\\ -x-2 =2x + 10\end{matrix}\right.$
$\Rightarrow \left[\begin{matrix} x -2x = 10 - 2\\ -x-2x =10+ 2\end{matrix}\right.$
$\Rightarrow \left[\begin{matrix}x = 8\\ -3x =12\end{matrix}\right.$
$\Rightarrow \left[\begin{matrix} x= 8(loại) \\ x = -4(tm)\end{matrix}\right.$
c) thay `x = -2` vào biểu thức
$\Rightarrow 2x -| x + 2| $
$\Rightarrow 2( -2) -| -2 + 2| $
$\Rightarrow -4 - 0$
$\Rightarrow -4$
mong hay nhất ạ~~
