Đáp án:
f) \(\left[ \begin{array}{l}
x = \dfrac{2}{3}\\
x = - \dfrac{2}{3}
\end{array} \right.\)
Giải thích các bước giải:
\(\begin{array}{l}
a)\dfrac{x}{7} = - \dfrac{9}{{21}}\\
\to x = - \dfrac{9}{{21}}.7\\
\to x = - 3\\
b)x = \dfrac{3}{5} + \dfrac{2}{3}\\
\to x = \dfrac{{20}}{{15}}\\
c)\left| {2x - 3} \right| = 13\\
\to \left[ \begin{array}{l}
2x - 3 = 13\\
2x - 3 = - 13
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = 8\\
x = - 5
\end{array} \right.\\
d)\left[ \begin{array}{l}
x = 0\\
x + 12 = 0
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = 0\\
x = - 12
\end{array} \right.\\
e)DK:x \ne 0\\
\dfrac{x}{3} = \dfrac{{12}}{x} \to {x^2} = 36\\
\to \left| x \right| = 6\\
\to \left[ \begin{array}{l}
x = 6\\
x = - 6
\end{array} \right.\\
f){x^2} = \dfrac{4}{9}\\
\to \left| x \right| = \dfrac{2}{3}\\
\to \left[ \begin{array}{l}
x = \dfrac{2}{3}\\
x = - \dfrac{2}{3}
\end{array} \right.\\
g)\dfrac{x}{{45}} = \dfrac{5}{6} - \dfrac{{29}}{{30}}\\
\to \dfrac{x}{{45}} = - \dfrac{2}{{15}}\\
\to x = - 6\\
d)\dfrac{x}{5} = \dfrac{1}{5}\\
\to x = 1
\end{array}\)
