* Đáp án
* Hướng dẫn giải
\({Z_\varepsilon } = \sqrt {\frac{{\left( {4 - {\varepsilon _\alpha }} \right)\left( {1 - {\varepsilon _\beta }} \right)}}{3} + \frac{{{\varepsilon _\beta }}}{{{\varepsilon _\alpha }}}}\) nếu εβ > 1 \(\Rightarrow {Z_\varepsilon } = \sqrt {\frac{1}{{{\varepsilon _\alpha }}}}\)