Hướng dẫn trả lời:
a) `-3x^2 + 5x + 2 = 0`
`→ -(3x^2 - 5x - 2) = 0`
`→ -(3x^2 - 6x + x - 2) = 0`
`→ -[3xcdot(x - 2) + (x - 2)] = 0`
`→ -(3x + 1)cdot(x - 2) = 0`
`→` \(\left[ \begin{array}{l}3x + 1 = 0\\x - 2 = 0\end{array} \right.\)
`→` \(\left[ \begin{array}{l}3x = - 1\\x = 2\end{array} \right.\)
`→` \(\left[ \begin{array}{l}x = \dfrac{- 1}{3}\\x = 2\end{array} \right.\)
Vậy `x = -1/3` hoặc `x = 2`
b) `4x^2 - 1 - xcdot(2x + 1) = 0`
`→ (2x)^2 - 1^2 - xcdot(2x + 1) = 0`
`→ (2x - 1)cdot(2x + 1) - xcdot(2x + 1) = 0`
`→ [(2x - 1) - x]cdot(2x + 1) = 0`
`→ (2x - 1 - x)cdot(2x + 1) = 0`
`→ (x - 1)cdot(2x + 1) = 0`
`→` \(\left[ \begin{array}{l}x - 1 = 0\\2x + 1 = 0\end{array} \right.\)
`→` \(\left[ \begin{array}{l}x = 1\\2x = -1\end{array} \right.\)
`→` \(\left[ \begin{array}{l}x = 1\\x = \dfrac{-1}{2}\end{array} \right.\)
Vậy `x = 1` hoặc `x = -1/2`
Đáp án:
a) `x = -1/3` hoặc `x = 2`
b) `x = 1` hoặc `x = -1/2`
