Đáp án: + Giải thích các bước giải:
`a//`
`5x = 8 + 3x`
`⇔ 5x - 3x = 8`
`⇔ 2x = 8`
`⇔ x = 4`
`b//`
`3x^2 + 9x = 0`
`⇔ 3x(x+3)=0`
`⇔` \(\left[ \begin{array}{l}4x=0\\x+3=0\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}x=0\\x=-3\end{array} \right.\)
`c//`
`(2x)/(x + 4) + 5/(x-2) = 2` `ĐKXĐ : x \ne -4;2`
`⇔ (2x(x-2))/((x+4)(x-2)) + (5(x+4))/((x-2)(x+4)) = (2(x-2)(x+4))/((x-2)(x+4))`
`⇔ 2(x-2) + 5(x + 4) = 2(x-2)(x+4)`
`⇔ 2x^2 + 20 + x = 2(x-2)(x+4)`
`⇔ 2x^2 + x - ( 2x^2 + 4x ) = 2x^2 + 4x - 36 ( 2x^2 + 4x )`
`⇔ -3x = -36`
`⇔ x = 12 \text{(thỏa mãn)}`
`d//`
`| x - 9 | = 2x + 5`
Trường hợp 1 :
`x - 9 = 2x + 5`
`⇔ x = 2x + 14`
`⇔ x - 2x = 14`
`⇔ -x = 14`
`⇔ x = -14`
Trường hợp 2 :
`x-9=-2x-5`
`⇔ x = -2x + 4`
`⇔ x + 2x = 4`
`⇔ 3x = 4`
`⇔ x = 4/3`
