Question : If $\sqrt{x}+\frac{1}{\sqrt{x}}=3, x>0$, then $x^2\left(x^2-47\right)=?$
Option 1: $0$
Option 2: $2$
Option 3: $-2$
Option 4: $-1$
Correct Answer: $-1$
Solution : As we know, $(x + \frac{1}{x})^2 = x^2 + \frac{1}{x^2} + 2$ ⇒ $(\sqrt{x} + \frac{1}{\sqrt{x}})^2 = x+\frac{1}{x} +2$ ⇒ $x + \frac{1}{x} + 2 = 3^2 = 9$ ⇒ $x + \frac{1}{x} = 9 - 2 = 7$ ⇒ $(x + \frac{1}{x})^2= 7^2$ ⇒ $x^2 + \frac{1}{x^2} + 2 = 49$ ⇒ $\frac{(x^4 + 1)}{x^2} = 49 - 2 = 47$ ⇒ $x^4 + 1 = 47x^2$ ⇒ $x^4 - 47x^2 = – 1$ ⇒ $x^2(x^2 - 47) = – 1$ Hence, the correct answer is $-1$.
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Question : If $x^2+\frac{1}{x^2}=\frac{7}{4}$ for $x>0$; then what is the value of $x+\frac{1}{x}$?
Option 1: $2$
Option 2: $\frac{\sqrt{15}}{2}$
Option 3: $\sqrt{5}$
Option 4: $\sqrt{3}$
Question : If $x^2+\frac{1}{x^2}=\frac{7}{4}$ for $x>0$, what is the value of $(x^3+\frac{1}{x^3})$?
Option 1: $\frac{3\sqrt{3}}{5}$
Option 2: $\frac{3\sqrt{15}}{5}$
Option 3: $\frac{3\sqrt{15}}{8}$
Option 4: $\frac{3\sqrt{5}}{8}$
Question : If $x^4+x^{-4}=47, x>0$, then what is the value of $x+\frac{1}{x}-2?$
Option 1: 1
Option 2: 0
Option 3: 5
Option 4: 3
Question : If $x^2-\sqrt{7} x+1=0$, then $\left(x^3+x^{-3}\right)=?$
Option 1: $4 \sqrt{7}$
Option 2: $3 \sqrt{7}$
Option 3: $10 \sqrt{7}$
Option 4: $7 \sqrt{7}$
Question : If $x^2-3 x+1=0$, then the value of $\left(x^4+\frac{1}{x^2}\right) \div\left(x^2+1\right)$ is:
Option 1: 5
Option 2: 6
Option 3: 9
Option 4: 7
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