If $a^4 +\frac{1}{a^4}$ = 194, then what is the value of $a^3 +\frac{1}{a^3}$ ?
Answer & explanation
Correct answer: option 2
If x4 + \(\frac{1}{x^4}\) = a
then x2 + \(\frac{1}{x^2}\) = \(\sqrt {a + 2}\) = b
and x + \(\frac{1}{x}\) = \(\sqrt {b + 2}\)
If $a^4 +\frac{1}{a^4}$ = 194
then x2 + \(\frac{1}{x^2}\) = \(\sqrt {194 + 2}\) = 14
and x + \(\frac{1}{x}\) = \(\sqrt {14 + 2}\) = 4
If x + \(\frac{1}{x}\) = n
then, $x^3 +\frac{1}{x^3}$ = n3 - 3 × n
$x^3 +\frac{1}{x^3}$ = 43 - 3 × 4 = 52