Nếu $K = \dfrac{{y + 81}}{{y - 81}}$ thì

$x > 3$

$x \ge 0;x \ne 9$       

$0 \le x < 9$

$x < 9$

$\dfrac{7}{{13}}$

$\dfrac{{3\sqrt 5  - 15}}{{10}}$

$\dfrac{7}{{33}}$

$\dfrac{{13}}{7}$

$P = \dfrac{3}{{\sqrt x  + 3}}$        

$P = \dfrac{{ - 3}}{{\sqrt x  + 3}}$

$P = \dfrac{{ - 3}}{{\sqrt x  - 3}}$

$P = \dfrac{3}{{\sqrt x  - 3}}$

$P = \dfrac{3}{{\sqrt x  + 3}}$        

$P = \dfrac{{ - 3}}{{\sqrt x  + 3}}$

$P = \dfrac{{ - 3}}{{\sqrt x  - 3}}$

$P = \dfrac{3}{{\sqrt x  - 3}}$

$K = \dfrac{{\sqrt x  + 9}}{{\sqrt x  - 9}}$

$K = \dfrac{{x - 9}}{{x + 9}}$

$K = \dfrac{{x + 9}}{{x - 9}}$

$K = \dfrac{1}{{\sqrt x  + 3}}$

$K = \dfrac{{\sqrt x  + 9}}{{\sqrt x  - 9}}$

$K = \dfrac{{x - 9}}{{x + 9}}$

$K = \dfrac{{x + 9}}{{x - 9}}$

$K = \dfrac{1}{{\sqrt x  + 3}}$