If $x^{2}- 5x + 1 = 0$, then the value of $\left(x^{4} + \frac{1}{x^{2}}\right) \div (x^{2} + 1)$ is:
Answer & explanation
Correct answer: option 2
If x + \(\frac{1}{x}\) = n
then, $x^3 +\frac{1}{x^3}$ = n3 - 3 × n
If $x^{2}- 5x + 1 = 0$
then the value of $\left(x^{4} + \frac{1}{x^{2}}\right) \div (x^{2} + 1)$ = ?
we can write $\left(x^{4} + \frac{1}{x^{2}}\right) \div (x^{2} + 1)$ by taking x as common form numerator and denominator as =
$\left(x^{3} + \frac{1}{x^{3}}\right) \div (x + \frac{1}{x})$
$x^{2}- 5x + 1 = 0$
Divide by x on both sides,
x + \(\frac{1}{x}\) = 5
then, $x^3 +\frac{1}{x^3}$ = 53 - 3 × 5 = 110
So the value of $\left(x^{3} + \frac{1}{x^{3}}\right) \div (x + \frac{1}{x})$ = \(\frac{110}{5}\) = 22