Đáp án đúng: A
Giải chi tiết:\(\begin{array}{l}\,\frac{3}{4} - \left( {x + \frac{1}{2}} \right) = \frac{4}{5}\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\left( {x + \frac{1}{2}} \right) = \frac{3}{4} - \frac{4}{5}\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x + \frac{1}{2}\,\,\,\, = \frac{{15 - 16}}{{20}}\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x + \frac{1}{2}\,\,\,\, = \frac{{ - 1}}{{20}}\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x\,\,\,\,\,\,\,\,\,\,\,\,\, = \frac{{ - 1}}{{20}} - \frac{1}{2}\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x\,\,\,\,\,\,\,\,\,\,\,\,\, = \,\,\frac{{ - 11}}{{20}}\end{array}\)
Chọn A