Đáp án:
8) \(x = \dfrac{2}{{19}}\)
Giải thích các bước giải:
\(\begin{array}{l}
1)5{x^2} - 15x + 5 + x - 5{x^2} - x + 2 = 0\\
\to 15x = 7\\
\to x = \dfrac{7}{{15}}\\
3){x^2} - 10x + 18 - {x^2} = 12\\
\to 10x = 6\\
\to x = \dfrac{3}{5}\\
5)4{x^2} - 20x - 7{x^2} + 28x + 3{x^2} = 12\\
\to 8x = 12\\
\to x = \dfrac{3}{2}\\
7) - 3{x^2} + 15x + 5x - 5 + 3{x^2} + x = 4\\
\to 21x = 9\\
\to x = \dfrac{3}{7}\\
2)12{x^2} - 12x + 20 = 10x - 17\\
\to 12{x^2} - 22x + 37 = 0\left( {vô lý} \right)\\
Do:12{x^2} - 22x + 37 > 0\left( {ld} \right)\forall x \in R
\end{array}\)
⇒ Phương tình vô nghiệm
\(\begin{array}{l}
4)4{x^2} + 3x - 4{x^2} + 8x = 10\\
\to 11x = 10\\
\to x = \dfrac{{10}}{{11}}\\
6)4{x^2} - 2x + 3 - 4{x^2} + 20x - 7x = - 7\\
\to 11x = - 10\\
\to x = - \dfrac{{10}}{{11}}\\
8)7{x^2} - 14x - 5x + 5 = 21{x^2} - 14{x^2} + 3\\
\to - 19x = - 2\\
\to x = \dfrac{2}{{19}}
\end{array}\)
