Rút gọn \(Q.\) A.\(Q = \frac{{\sqrt x }}{{\sqrt x - 2}}\) B.\(Q = \frac{{\sqrt x }}{{\sqrt x + 2}}\) C.\(Q = \frac{{\sqrt x + 2}}{{\sqrt x - 2}}\) D.\(Q = \frac{{\sqrt x - 2}}{{\sqrt x + 2}}\)
Đáp án đúng: A Giải chi tiết:Điều kiện: \(x > 0,\,\,\,x \ne 4.\) \(\begin{array}{l}Q = \frac{{\sqrt x - 1}}{{\sqrt x + 2}} + \frac{{5\sqrt x - 2}}{{x - 4}} = \frac{{\sqrt x - 1}}{{\sqrt x + 2}} + \frac{{5\sqrt x - 2}}{{\left( {\sqrt x + 2} \right)\left( {\sqrt x - 2} \right)}}\\\,\,\,\,\, = \frac{{\left( {\sqrt x - 1} \right)\left( {\sqrt x - 2} \right) + 5\sqrt x - 2}}{{\left( {\sqrt x + 2} \right)\left( {\sqrt x - 2} \right)}} = \frac{{x - 3\sqrt x + 2 + 5\sqrt x - 2}}{{\left( {\sqrt x + 2} \right)\left( {\sqrt x - 2} \right)}}\\\,\,\,\,\, = \frac{{x + 2\sqrt x }}{{\left( {\sqrt x + 2} \right)\left( {\sqrt x - 2} \right)}} = \frac{{\sqrt x \left( {\sqrt x + 2} \right)}}{{\left( {\sqrt x + 2} \right)\left( {\sqrt x - 2} \right)}} = \frac{{\sqrt x }}{{\sqrt x - 2}}.\end{array}\) Chọn A.