Đáp án: + Giải thích các bước giải:
`a) 3x(8x-4)-6x(4x-3)=30`
`⇔ 24x^2 - 12x - 24x^2 + 18x = 30`
`⇔ 6x = 30`
`⇔ x = 5`
Vậy `S = {5}`
`b) (8x-3)(3x+2)-(4x+7)(x+4)=(2x+1)(5x-1)`
`⇔ 20x^2 - 16x - 34 = 10x^2 + 3x - 1`
`⇔ 20x^2 - 16x - 33 = 10x^2 + 3x`
`⇔ 20x^2 - 19x - 33 = 10x^2`
`⇔ 10x^2 - 19x - 33 = 0`
`⇔ x(10x+11)-3(10x+11) = 0`
`⇔ (10x+11)(x-3) = 0`
`⇔`\(\left[ \begin{array}{l}10x+11=0\\x-3=0\end{array} \right.\)
`⇔`\(\left[ \begin{array}{l}x=-\dfrac{11}{10}\\x=3\end{array} \right.\)
Vậy `S = {-11/10,3}`
`c) (2x-1)^2 - (2x+3)(2x-1)=0`
`⇔ 4x^2 - 4x + 1 - 4x^2 - 4x + 3 = 0`
`⇔ -8x + 4 = 0`
`⇔ -8x = -4`
`⇔ x = 1/2`
Vậy `S = {1/2}`
`d) (x+5)(x-2)-(x-3)(x+3)=0`
`⇔ x^2 + 3x - 10 - x^2 + 9 =0`
`⇔ 3x - 1 = 0`
`⇔ 3x = 1`
`⇔ x = 1/3`
Vậy `S = {1/3}`
