If $x^4 + x^{− 4} = 47$, x > 0, then what is the value of $x+\frac{1}{x}-2$?
Answer & explanation
Correct answer: option 1
If x4 + \(\frac{1}{x^4}\) = a
then x2 + \(\frac{1}{x^2}\) = \(\sqrt {a + 2}\) = b
and x + \(\frac{1}{x}\) = \(\sqrt {b + 2}\)
According to the question,
$x^4 + x^{− 4} = 47$
x2 + \(\frac{1}{x^2}\) = \(\sqrt {47 + 2}\) = 7
and x + \(\frac{1}{x}\) = \(\sqrt {7 + 2}\) = 3
$x+\frac{1}{x}-2$ = 3 - 2 = 1