Đáp án:
Giải thích các bước giải:
` a) x² - 6x + 8 = 0`
`x² - 4x - 2x + 8 = 0`
`x(x-4) - 2(x-4) = 0`
`(x-4)(x-2) = 0`
\(\left[ \begin{array}{l}x=4\\x=2\end{array} \right.\)
`b) x² + 5x - 6 = 0`
`x² - x + 6x - 6 = 0`
x(x-1) + 6(x-1) = 0`
`(x-1)(x+6) = 0`
\(\left[ \begin{array}{l}x=1\\x=-6\end{array} \right.\)
`c) x² - 4x - 5 = 0`
`x² - 5x + x - 5 = 0`
`x(x-5) + (x-5) = 0`
`(x-5)(x+1) = 0`
\(\left[ \begin{array}{l}x=5\\x=-1\end{array} \right.\)
`d) 2x² - 5x + 3 = 0`
`2x² - 2x - 3x + 3 = 0`
`2x(x-1) - 3(x-1) = 0`
`(x-1)(2x - 3)= 0`
\(\left[ \begin{array}{l}x=\dfrac{3}{2}\\x=1\end{array} \right.\)
`e) 5x² + 7x + 2 = 0`
`5x² + 2x + 5x + 2 = 0`
`x(5x + 2) + (5x + 2) = 0`
`(x+1)(5x + 2) = 0`
\(\left[ \begin{array}{l}x=\dfrac{-2}{5}\\x=-1\end{array} \right.\)
