Question : If $\left (x+\frac{1}{x} \right)=5$, what is the value of $\left (x^{5}+\frac{1}{x^{5}} \right)$?
Option 1: 1875
Option 2: 2525
Option 3: 2530
Option 4: 3120
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Correct Answer: 2525
Solution :
Given: $\left (x+\frac{1}{x} \right)=5$
Squaring both sides, we get,
$⇒\left (x+\frac{1}{x} \right )^{2}=5^{2}$
$⇒x^{2}+\frac{1}{x^{2}}+2=25$
$⇒x^{2}+\frac{1}{x^{2}}=23$
Also, $\left ( x+\frac{1}{x} \right )^{3}=5^{3}$
$⇒x^{3}+\frac{1}{x^{3}}+3(x)(\frac{1}{x})(x+\frac{1}{x})=125$
$⇒x^{3}+\frac{1}{x^{3}}+3(1)(5)=125$
$⇒x^{3}+\frac{1}{x^{3}}=110$
Now, $(x^{3}+\frac{1}{x^{3}})( x^2+\frac{1}{x^2})=x^{5}+\frac{1}{x^{5}}+x+\frac{1}{x}$
$⇒110\times 23=x^{5}+\frac{1}{x^{5}}+5$
$\therefore x^{5}+\frac{1}{x^{5}} = 2525$
Hence, the correct answer is 2525.
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