Đáp án:
b) x=-9
Giải thích các bước giải:
\(\begin{array}{l}
d)\dfrac{{6\left( {x - 4} \right) + 3\left( {3x - 2} \right) - 30x - 10\left( {2x - 5} \right) + 5\left( {7x + 2} \right)}}{{30}} = 0\\
\to 6x - 24 + 9x - 6 - 30x - 20x + 50 + 35x + 10 = 0\\
\to 0x = - 30\left( {vô lý} \right)
\end{array}\)
⇒ Phương trình vô nghiệm
\(\begin{array}{l}
a)\dfrac{{4\left( {{x^2} + 8x - 20} \right) - {x^2} - 14x - 40 - 3\left( {{x^2} + 2x - 8} \right)}}{{12}} = 0\\
\to 4{x^2} + 32x - 80 - {x^2} - 14x - 40 - 3{x^2} - 6x + 24 = 0\\
\to 12x = 96\\
\to x = 8\\
c)\dfrac{{3\left( {4{x^2} - 9} \right) - 4\left( {{x^2} - 8x + 16} \right) - 8\left( {{x^2} - 4x + 4} \right)}}{{24}} = 0\\
\to 12{x^2} - 27 - 4{x^2} + 32x - 64 - 8{x^2} + 32x - 32 = 0\\
\to 64x = 123\\
\to x = \dfrac{{123}}{{64}}\\
b)\dfrac{{{x^2} + 4x + 4 - 16\left( {2x + 1} \right) - 25.8 - {x^2} + 4x - 4}}{8} = 0\\
\to - 24x = 216\\
\to x = - 9\\
d)\dfrac{{7{x^2} - 14x - 5 - 3\left( {4{x^2} + 4x + 1} \right) + 5\left( {{x^2} - 2x + 1} \right)}}{{15}} = 0\\
\to 7{x^2} - 14x - 5 - 12{x^2} - 12x - 3 + 5{x^2} - 10x + 5 = 0\\
\to - 36x = 3\\
\to x = - \dfrac{1}{{12}}
\end{array}\)
