Đáp án:
b) x=16
Giải thích các bước giải:
\(\begin{array}{l}
a)P = \dfrac{{\left( {\sqrt x + 1} \right)\left( {\sqrt x + 3} \right) + 2\sqrt x \left( {\sqrt x - 3} \right) - 7\sqrt x - 3}}{{\left( {\sqrt x + 3} \right)\left( {\sqrt x - 3} \right)}}\\
= \dfrac{{x + 4\sqrt x + 3 + 2x - 6\sqrt x - 7\sqrt x - 3}}{{\left( {\sqrt x + 3} \right)\left( {\sqrt x - 3} \right)}}\\
= \dfrac{{3x - 9\sqrt x }}{{\left( {\sqrt x + 3} \right)\left( {\sqrt x - 3} \right)}} = \dfrac{{3\sqrt x }}{{\sqrt x + 3}}\\
b)P = \dfrac{{12}}{7}\\
\to \dfrac{{3\sqrt x }}{{\sqrt x + 3}} = \dfrac{{12}}{7}\\
\to 21\sqrt x = 12\sqrt x + 36\\
\to 9\sqrt x = 36\\
\to \sqrt x = 4\\
\to x = 16
\end{array}\)
