\(B=\dfrac{\sqrt{x}+5+\sqrt{x}-5-10}{\left(\sqrt{x}-5\right)\left(\sqrt{x}+5\right)}\)
\(B=\dfrac{2\sqrt{x}-10}{\left(\sqrt{x}+5\right)\left(\sqrt{x}-5\right)}=\dfrac{2\left(\sqrt{x}-5\right)}{\left(\sqrt{x}-5\right)\left(\sqrt{x}+5\right)}\)
B=\(\dfrac{2}{\sqrt{x}+5}\)
b)thay x=50 vào biểu thức
B=\(\dfrac{2}{\sqrt{50}+5}\)=\(\dfrac{2\left(\sqrt{50}-5\right)}{\left(\sqrt{50}+5\right)\left(\sqrt{50}-5\right)}=\dfrac{2\sqrt{50}-10}{25}\)
c)để B>\(\dfrac{1}{6}\)
\(\dfrac{2}{\sqrt{x}+5}>\dfrac{1}{6}\Rightarrow12>\sqrt{x}+5\)
\(\sqrt{x}< 7\Rightarrow x< 49\)
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