Đáp án + Giải thích các bước giải:
19)
`(2x-1)² - (5x - 5)² = 0`
`(2x - 1 - 5x + 5)(2x - 1 + 5x - 5) = 0`
`(-3x + 4)(7x - 6) = 0`
\(\left[ \begin{array}{l}x=\dfrac{4}{3}\\x=\dfrac{6}{7}\end{array} \right.\)
⇒ C
20)
`(2x + 1)² - 4(x + 2)² = 0`
`(2x + 1)² - [2(x+2)]² = 0`
`(2x + 1 - 4x - 4)(2x + 1 + 4x + 4) = 0`
`(-2x - 3)(6x + 5) = 0`
\(\left[ \begin{array}{l}x=\dfrac{-3}{2}\\x=\dfrac{-5}{6}\end{array} \right.\)
⇒ C
21)
`(x-6)(x+6) - (x+3)² = 9`
`x² - 36 - x² - 6x - 9 - 9 = 0`
`-6x - 54 = 0`
`6x = -54`
`x = -9`
`⇒ A`
22)
`(3x - 1)² + 2(x+3)² + 11(1+x)(1-x) = 6`
`9x² - 6x + 1 + 2(x² + 6x + 9) + 11(1 - x²) = 6`
`9x² - 6x + 1 + 2x² + 12x + 18 + 11 - 11x² = 6`
`6x + 24 = 0`
`6x = -24`
`x = -4`
`⇒ B`
