solve this
Question:

If $x=(7+4 \sqrt{3})$ then $\left(x+\frac{1}{x}\right)=?$

(a) $8 \sqrt{3}$

(b) 14

(c) 49

(d) 48

 

Solution:

Given: $x=(7+4 \sqrt{3})$

$\frac{1}{x}=\frac{1}{7+4 \sqrt{3}}=\frac{1}{7+4 \sqrt{3}} \times \frac{7-4 \sqrt{3}}{7-4 \sqrt{3}}=\frac{7-4 \sqrt{3}}{49-48}=7-4 \sqrt{3}$

$\left(x+\frac{1}{x}\right)=7+4 \sqrt{3}+(7-4 \sqrt{3})=14$

Hence, the correct answer is option (b). 

 

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