If $x^2 - 4x + 1 = 0$, then what is the value of $(x^6 + x^{-6})$?
Answer & explanation
Correct answer: option 2
If $K+\frac{1}{K}=n$
then, $K^2+\frac{1}{K^2}$ = n2 – 2
If x + \(\frac{1}{x}\) = n
then, $x^3 +\frac{1}{x^3}$ = n3 - 3 × n
If $x^2 - 4x + 1 = 0$
Then what is the value of $(x^6 + x^{-6})$
Divide by x on both sides of $x^2 - 4x + 1 = 0$
x + \(\frac{1}{x}\) = 4
$x^2+\frac{1}{x^2}$ = 42 – 2 = 14
Now cubing on both sides,
$x^6+\frac{1}{x^6}$ = 143 - 3 × 14
$x^6+\frac{1}{x^6}$ =2744 - 42 = 2702