Đáp án:
d. \(\left[ \begin{array}{l}
x = - 3\\
x = - 2
\end{array} \right.\)
Giải thích các bước giải:
\(\begin{array}{l}
a.\left( {5x - 55} \right)\left( {x + 20} \right) = 0\\
\to \left[ \begin{array}{l}
5x - 55 = 0\\
x + 20 = 0
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = 11\\
x = - 20
\end{array} \right.\\
b.3x - 9 + 6x - 6 = 2\\
\to 9x = 17\\
\to x = \dfrac{{17}}{9}\\
c.5\left( {x - 4} \right) + 2\left( {x + 7} \right) = 15\\
\to 5x - 20 + 2x + 14 = 15\\
\to 7x = 21\\
\to x = 3\\
d.\left( {x + 3} \right)\left( {4x + 8} \right) = 0\\
\to \left[ \begin{array}{l}
x + 3 = 0\\
4x + 8 = 0
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = - 3\\
x = - 2
\end{array} \right.
\end{array}\)
