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19+6+19−6\frac{1}{9 + \sqrt{6}} + \frac{1}{9 - \sqrt{6}}9+6​1​+9−6​1​ = ?
Question

19+6+196\frac{1}{9 + \sqrt{6}} + \frac{1}{9 - \sqrt{6}} = ?

A.

7/24

B.

9/25

C.

6/25

D.

9/19

Correct option is C

Given:
Expression: 19+6+196\frac{1}{9 + \sqrt{6}} + \frac{1}{9 - \sqrt{6}}​​
Formula Used:
1a+b+1ab=2aa2b2\frac{1}{a + b} + \frac{1}{a - b} = \frac{2a}{a^2 - b^2}​​
Solution:
19+6+196 =1(9+6)(96) =96+9+6(9)2(6)2 =9+9816 =1875=625\frac{1}{9 + \sqrt{6}} + \frac{1}{9 - \sqrt{6}} \\ \ \\ = \frac{1}{(9 + \sqrt{6})(9 - \sqrt{6})} \\ \ \\ = \frac{9 - \sqrt{6} + 9 + \sqrt{6}}{(9)^2 - (\sqrt{6})^2} \\ \ \\ = \frac{9 + 9}{81 -6} \\ \ \\ = \frac{18}{75} = \frac{6}{25}​​
Final Answer
So the correct answer is (c)

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