2 câu trả lời
\[\begin{array}{l} \frac{{11}}{{12}} - \left( {\frac{2}{5} + x} \right) = \frac{2}{3}\\ \frac{2}{5} + x = \frac{2}{3} - \frac{{11}}{{12}}\\ \frac{2}{5} + x = - \frac{1}{4}\\ x = - \frac{1}{4} - \frac{2}{5} = - \frac{{13}}{{20}}.\\ \frac{3}{4} + \frac{1}{4}:x = \frac{2}{3}\\ \frac{1}{4}:x = \frac{2}{3} - \frac{3}{4}\\ \frac{1}{4}:x = - \frac{1}{{12}}\\ x = \frac{1}{4}:\frac{{ - 1}}{{12}} = - 3. \end{array}\]
a) 11/12 - (2/5 + x) = 2/3
<-> 11/12 - 2/5 - x = 2/3
<-> 55/60 - 24/60 - x - 46/60 = 0
<-> x = -1/4
b) 3/4 + 1/4 :x = 2/3
<-> 1/4:x = 2/3 - 3/4
<-> 1/4:x = 8/12 - 9/12
<-> 1/4:x = -1/12
<-> x = 1/4 : (-1/12)
<-> x = -3.
