1: Khi x=100 thì \(A=\dfrac{100+24}{10-2}=\dfrac{124}{8}=15.5\)
2: \(B=\dfrac{\sqrt{x}+3}{\sqrt{x}+1}+\dfrac{2}{\sqrt{x}-3}-\dfrac{7\sqrt{x}-13}{x-2\sqrt{x}-3}\)
\(=\dfrac{\left(\sqrt{x}+3\right)\left(\sqrt{x}-3\right)+2\left(\sqrt{x}+1\right)-7\sqrt{x}+13}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+1\right)}\)
\(=\dfrac{x-9+2\sqrt{x}+2-7\sqrt{x}+13}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+1\right)}\)
\(=\dfrac{x-5\sqrt{x}+6}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+1\right)}=\dfrac{\left(\sqrt{x}-2\right)\left(\sqrt{x}-3\right)}{\left(\sqrt{x}-3\right)\left(\sqrt{x}+1\right)}\)
\(=\dfrac{\sqrt{x}-2}{\sqrt{x}+1}\)
4: |B|>-B
=>B>0
=>(căn x-2)/(căn x+1)>0
=>căn x-2>0
=>x>4
