`a, 3x + 9 = 0`
`⇔ 3(x + 3) = 0`
`⇔ x + 3 = 0`
`⇔ x = -3`
`b, (x - 1)^2 - 4 = 0`
`⇔ (x - 1)^2 - 2^2 = 0`
`⇔ (x - 1 - 2)(x - 1 + 2) = 0`
`⇔ (x - 3)(x + 1) = 0`
`⇔` \(\left[ \begin{array}{l}x-3=0\\x+1=0\end{array} \right.\) `⇔` \(\left[ \begin{array}{l}x=3\\x=-1\end{array} \right.\)
`c, \frac{x+3}{x+1} + \frac{x-2}{x} = 1` `(đk: x \ne 0; x \ne -1)`
`⇔ \frac{x(x+3)}{x(x+1)} + \frac{(x-2)(x+1)}{x(x+1)} = \frac{x+1}{x+1}`
`⇒ x(x + 3) + (x - 2)(x + 1) = x + 1`
`⇔ x^2 + 3x + x^2 + x - 2x - 2 = x + 1`
`⇔ 2x^2 + x - 3 = 0`
`⇔ 2x^2 + 3x - 2x - 3 = 0`
`⇔ 2x(x - 1) + 3(x - 1) = 0`
`⇔ (2x + 3)(x - 1) = 0`
`⇔` \(\left[ \begin{array}{l}2x+3=0\\x-1=0\end{array} \right.\) `⇔` \(\left[ \begin{array}{l}x=\dfrac{-3}{2}(TM)\\x=1(TM)\end{array} \right.\)
`d, |x + 2| = 10`
`⇔` \(\left[ \begin{array}{l}x+2=10\\x+2=-10\end{array} \right.\) `⇔` \(\left[ \begin{array}{l}x=8\\x=-12\end{array} \right.\)
`e, 2(1 - 2x) ≥ 4 - 5x`
`⇔ 2 - 4x ≥ 4 - 5x`
`⇔ x ≥ 2`
