If x>1, and x⁴+1 over x⁴=79 , what is the value of x-1 over x?

SSC Selection Post 2023 PYQ — Question 51

If ${{x>1, }}$ and $x^4+{{1} \over x^4}=79$ , what is the value of $x-{{1} \over x}?$

Show answer & explanation

Correct answer: B

Explanation

The correct answer is Option 2 i.e. ${{\sqrt7}}$ .

x⁴ + 1/x⁴ = 79

⇒ x² + 1/x² = √(79 + 2) = 9

⇒ x - 1/x = √(9 - 2) = √7