Question : If $x+\frac{1}{x}=-14$, and $x<-1$, what will be the value of $x^2-\frac{1}{x^2}$?
Option 1: $-112 \sqrt{3}$
Option 2: $112 \sqrt{3}$
Option 3: $-140 \sqrt{2}$
Option 4: $140 \sqrt{2}$
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Correct Answer: $112 \sqrt{3}$
Solution : Given, $x+\frac{1}{x}=-14$ Squaring both sides, we get, ⇒ $x^2+\frac{1}{x^2}+2=196$ ⇒ $x^2+\frac{1}{x^2}=196-2=194$ Subtracting 2 from both sides, we get, $x^2+\frac{1}{x^2}-2=194-2$ ⇒ $(x-\frac{1}{x})^2=192$ ⇒ $x-\frac{1}{x}=-\sqrt{192}$ [as $x<-1$] Now $x^2-\frac{1}{x^2}$ $=(x-\frac{1}{x})(x+\frac{1}{x})$ $=(-\sqrt{192})\times (-14)$ $=8\sqrt3\times 14 = 112\sqrt3$ Hence, the correct answer is $112\sqrt3$.
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Question : If $\left(x^2+\frac{1}{x^2}\right)=7$, and $0<x<1$, find the value of $x^2-\frac{1}{x^2}$.
Option 1: $3 \sqrt{5}$
Option 2: $4 \sqrt{5}$
Option 3: $-4\sqrt{3}$
Option 4: $-3\sqrt{5}$
Question : If $\left(x^2+\frac{1}{x^2}\right)=6$ and $0<x<1$, what is the value of $x^4-\frac{1}{x^4}$?
Option 1: $24\sqrt{2}$
Option 2: $-24\sqrt{2}$
Option 3: $-12\sqrt{10}$
Option 4: $12\sqrt{10}$
Question : If $x^2-7 x+1=0$ and $0<x<1$, what is the value of $x^2-\frac{1}{x^2}?$
Option 1: $21\sqrt{5}$
Option 2: $-21\sqrt{5}$
Option 3: $28\sqrt{5}$
Option 4: $-28\sqrt{5}$
Question : If $\frac{\sqrt{5+x}+\sqrt{5-x}}{\sqrt{5+x}-\sqrt{5-x}}=3$, what is the value of $x$?
Option 1: $\frac{5}{2}$
Option 2: $\frac{25}{3}$
Option 3: $4$
Option 4: $3$
Question : If $\left(x+\frac{1}{x}\right)=\sqrt{6}$ and $x>1$, what is the value of $\left(x^8-\frac{1}{x^8}\right)$?
Option 1: $120\sqrt{3}$
Option 2: $128\sqrt{3}$
Option 3: $112\sqrt{3}$
Option 4: $108\sqrt{3}$
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