Giải thích các bước giải:

a.Ta có: $x=16\to \sqrt{x}=4$ 

$\to B=\dfrac{3\cdot 4-2}{1-4}=\dfrac{-10}3$

b.Ta có:

$B=\dfrac{15\sqrt{x}-11}{x+2\sqrt{x}-3}-\dfrac{2\sqrt{x}+3}{\sqrt{x}+3}$

$\to B=\dfrac{15\sqrt{x}-11}{(\sqrt{x}+3)(\sqrt{x}-1)}-\dfrac{(2\sqrt{x}+3)(\sqrt{x}-1)}{(\sqrt{x}+3)(\sqrt{x}-1)}$

$\to B=\dfrac{15\sqrt{x}-11-(2\sqrt{x}+3)(\sqrt{x}-1)}{(\sqrt{x}+3)(\sqrt{x}-1)}$

$\to B=\dfrac{-2x+14\sqrt{x}-8}{(\sqrt{x}+3)(\sqrt{x}-1)}$

$\to P=\dfrac{3\sqrt{x}-2}{1-\sqrt{x}}+ \dfrac{-2x+14\sqrt{x}-8}{(\sqrt{x}+3)(\sqrt{x}-1)}$

$\to P=-\dfrac{(\sqrt{x}+3)(3\sqrt{x}-2)}{(\sqrt{x}-1)(\sqrt{x}+3)}+ \dfrac{-2x+14\sqrt{x}-8}{(\sqrt{x}+3)(\sqrt{x}-1)}$

$\to P=\dfrac{-(\sqrt{x}+3)(3\sqrt{x}-2)-2x+14\sqrt{x}-8}{(\sqrt{x}+3)(\sqrt{x}-1)}$

$\to P=\dfrac{-5x+7\sqrt{x}-2}{(\sqrt{x}+3)(\sqrt{x}-1)}$

$\to P=\dfrac{-(5\sqrt{x}-2)(\sqrt{x}-1)}{(\sqrt{x}+3)(\sqrt{x}-1)}$ 

$\to P=\dfrac{-5\sqrt{x}+2}{\sqrt{x}+3}$

c.Ta có: $P(\sqrt{x}+3)=-5\sqrt{x}+2$

$\to m=-5\sqrt{x}+2$