Đáp án:
c. \(\left[ \begin{array}{l}
x = \dfrac{5}{2}\\
x = \dfrac{{17}}{6}
\end{array} \right.\)
Giải thích các bước giải:
\(\begin{array}{l}
a.\left[ \begin{array}{l}
{x^2} - 9 = 0\\
4 - x = 0
\end{array} \right. \to \left[ \begin{array}{l}
\left( {x - 3} \right)\left( {x + 3} \right) = 0\\
x = 4
\end{array} \right.\\
\to \left[ \begin{array}{l}
x - 3 = 0\\
x + 3 = 0\\
x = 4
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = 3\\
x = - 3\\
x = 4
\end{array} \right.\\
b.\left[ \begin{array}{l}
5x + 3 = 0\\
\dfrac{{3x + 11}}{4} - \dfrac{{x - 7}}{{12}} = 0
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = - \dfrac{3}{5}\\
3\left( {3x + 11} \right) - x + 7 = 0
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = - \dfrac{3}{5}\\
9x + 33 - x + 7 = 0
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = - \dfrac{3}{5}\\
8x = - 40
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = - \dfrac{3}{5}\\
x = - 5
\end{array} \right.\\
c.\left[ \begin{array}{l}
4x - 10 = 0\\
\dfrac{{4x - 3}}{5} - \dfrac{{2x + 6}}{7} = 0
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = \dfrac{5}{2}\\
7\left( {4x - 3} \right) - 5\left( {2x + 6} \right) = 0
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = \dfrac{5}{2}\\
28x - 21 - 10x - 30 = 0
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = \dfrac{5}{2}\\
18x = 51
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = \dfrac{5}{2}\\
x = \dfrac{{17}}{6}
\end{array} \right.
\end{array}\)
