Question: If $ \frac{\frac{1}{\sqrt{9}}-\frac{1}{\sqrt{11}}}{\frac{1}{\sqrt{9}}+\frac{1}{\sqrt{11}}}\times \frac{10+\sqrt{99}}{x}=\frac{1}{2}, $ then the value of $ x $ is
Options:
A) 2
B) 3
C) 4
D) 5
Show Answer
Answer:
Correct Answer: A
Solution:
- $ \frac{\frac{1}{\sqrt{9}}-\frac{1}{\sqrt{11}}}{\frac{1}{\sqrt{9}}+\frac{1}{\sqrt{11}}}=\frac{\sqrt{11}-\sqrt{9}}{\sqrt{11}+\sqrt{9}}=\frac{\sqrt{11}-\sqrt{9}}{\sqrt{11}+\sqrt{9}}\times \frac{\sqrt{11}-\sqrt{9}}{\sqrt{11}-\sqrt{9}} $
$ =\frac{11+9-2\sqrt{99}}{11-9}=\frac{2(10-\sqrt{99})}{2}=10-\sqrt{99} $
$ \therefore $ $ \frac{(10-\sqrt{99})\times (10+\sqrt{99})}{x}=\frac{1}{2} $
$ \Rightarrow $ $ \frac{100-99}{x}=\frac{1}{2} $
$ \Rightarrow $ $ \frac{1}{x}=\frac{1}{2} $
$ \Rightarrow $ $ x=2 $