Đáp án:
c) \(\sqrt x \)
Giải thích các bước giải:
\(\begin{array}{l}
C13:\\
a)DK:x \ge 1\\
b)\sqrt 3 + 2\sqrt 3 - 4\sqrt 3 + 5\sqrt 3 = 4\sqrt 3 \\
c)A = \left[ {\dfrac{{\sqrt x \left( {\sqrt x - 3} \right) + \sqrt x \left( {\sqrt x + 3} \right)}}{{\left( {\sqrt x - 3} \right)\left( {\sqrt x + 3} \right)}}} \right].\dfrac{{\left( {\sqrt x - 3} \right)\left( {\sqrt x + 3} \right)}}{{2\sqrt x }}\\
= \dfrac{{x - 3\sqrt x + x + 3\sqrt x }}{{\left( {\sqrt x - 3} \right)\left( {\sqrt x + 3} \right)}}.\dfrac{{\left( {\sqrt x - 3} \right)\left( {\sqrt x + 3} \right)}}{{2\sqrt x }}\\
= \dfrac{{2x}}{{2\sqrt x }} = \sqrt x
\end{array}\)
