$\text{Bài 1a) ( x+2 )² - x( x+2 ) = 0}$
$\text{⇔ ( x+2 )( x+2-x ) = 0}$
$\text{⇔ 2( x+2 ) = 0}$
$\text{⇔ x+2 = 0}$
$\text{⇔ x = -2}$
$\text{b) $\frac{2x+7}{3}$ - $\frac{x-2}{4}$ = 2}$
$\text{⇔ 4( 2x+7 ) - 3( x-2 ) = 2. 12}$
$\text{⇔ 8x + 28 - 3x + 6 = 24}$
$\text{⇔ 5x + 34 = 24}$
$\text{⇔ 5x = -10}$
$\text{⇔ x = -2}$
$\text{c) | x + 5| = 3x + 1}$
$\text{⇔ $\left \{ {{3x+1 ≥ 0} \atop {\left[ \begin{array}{l}x+5=-3x-1\\x+5 =3x+1\end{array} \right.}} \right.$ }$
$\text{⇔ $\left \{ {{x ≥ \frac{-1}{3} } \atop {\left[ \begin{array}{l}x= -2 (nhận)\\x=2(nhận)\end{array} \right. }} \right.$ }$
$\text{⇒ x = ±2}$
$\text{Bài 2 : 5x-2 ≤ 2x+8}$
$\text{⇔ 3x ≤ 10}$
$\text{⇔ x ≤ $\frac{10}{3}$ }$
$\text{b) $\frac{1}{5}a$ - 4 < $\frac{1}{5}b$ - 4 }$
$\text{⇔ $\frac{1}{5}a$ < $\frac{1}{5}b$ }$
$\text{⇔ a < b}$
$\text{c) Ta có : (a+b)²≥4ab}$
$\text{⇔ a²+2ab+b²≥4ab}$
$\text{⇔ a² +2ab+b² - 4ab≥ 0}$
$\text{⇔ a² - 2ab + b² ≥0}$
$\text{⇔ (a-b)² ≥ 0 (đúng)}$
$\text{Vậy (a+b)² ≥ 4ab}$