`a) 1/2 + 2/3x = 1/4`
<=> `2/3x = -1/4`
<=>`x = (-1/4) : 2/3`
<=> ` x = -3/8`
Vậy `x = -3/8`
b) `3/4 + 1/4 : x = -3`
<=> `1/4 : x = -15/4`
<=> `x = 1/4 : (-15/4)`
<=> `x = -1/15`
Vậy `x = -1/15`
c) `x (x + 2/3) = 0`
<=> \(\left[ \begin{array}{l}x=0\\x+\frac{2}{3} = 0\end{array} \right.\)
<=> \(\left[ \begin{array}{l}x=0\\x=-\frac{2}{3}\end{array} \right.\)
Vậy ...
d) ` (-3x)/4 . (1/x + 2/7) = 0`
<=> \(\left[ \begin{array}{l}-\frac{3x}{4} = 0\\\frac{1}{x}+\frac{2}{7} = 0\end{array} \right.\)
<=> \(\left[ \begin{array}{l}x = 0\\x = -3 ,5\end{array} \right.\)