a: Thay x=16 vào A, ta được:
\(A=\dfrac{4}{4-3}=4\)
b: Ta có: M=A-B
\(=\dfrac{\sqrt{x}}{\sqrt{x}-3}-\dfrac{7}{\sqrt{x}+1}+\dfrac{12}{\left(\sqrt{x}+1\right)\left(\sqrt{x}-3\right)}\)
\(=\dfrac{x+\sqrt{x}-7\sqrt{x}+21+12}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+1\right)}\)
\(=\dfrac{x-6\sqrt{x}+33}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+1\right)}\)
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