Đáp án:
Câu 2:
b) x=-15
Giải thích các bước giải:
\(\begin{array}{l}
C1:\\
a)Thay:x = 1\\
Pt \to {3.1^2} - m\left( {1 - 3} \right) + 5 = 0\\
\to 2m + 8 = 0\\
\to m = - 4\\
b)Thay:m = - 4\\
Pt \to 3{x^2} + 4\left( {x - 3} \right) + 5 = 0\\
\to 3{x^2} + 4x - 7 = 0\\
\to 3{x^2} - 3x + 7x - 7 = 0\\
\to 3x\left( {x - 1} \right) + 7\left( {x - 1} \right) = 0\\
\to \left( {x - 1} \right)\left( {3x + 7} \right) = 0\\
\to \left[ \begin{array}{l}
x = 1\\
x = - \dfrac{7}{3}
\end{array} \right.\\
C2:\\
a)\left( {x - 2} \right)\left( {3x - 1} \right) - 2\left( {x - 2} \right) = 0\\
\to \left( {x - 2} \right)\left( {3x - 1 - 2} \right) = 0\\
\to \left[ \begin{array}{l}
x - 2 = 0\\
3x - 3 = 0
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = 2\\
x = 1
\end{array} \right.\\
b)DK:x \ne \pm 2\\
\dfrac{{x - 2 - 5\left( {x + 2} \right) + x - 3}}{{\left( {x - 2} \right)\left( {x + 2} \right)}} = 0\\
\to 2x - 5 - 5x - 10 = 0\\
\to 3x = - 15\\
\to x = - 5
\end{array}\)
