Question

Which of the following are quadratic equation in x? 

`x^2 - 1/x^2 = 5`

Answer 1

`x^2 - 1/x^2 = 5x^2` 

⇒ x⁴ – 1 = 5x² 

⇒ x⁴ – 5x² – 1 = 0 

(x⁴ – 5x² – 1) is a polynomial with degree 4. 

∴ x² – 5x² – 1 = 0 is not a quadratic equation.