x2 + \(\frac{1}{x^2}\) = 98 (x > 0), then find the value of x5 + \(\frac{1}{x^5}\).
Answer & explanation
Correct answer: option 3
x2 + \(\frac{1}{x^2}\) = 98
(x + \(\frac{1}{x}\)) = \(\sqrt {98\;+\;2}\) = 10
x3 + \(\frac{1}{x^3}\) = 1000 - 3(10) = 970
Now, x5 + \(\frac{1}{x^5}\) = (x2 + \(\frac{1}{x^2}\)) (x3 + \(\frac{1}{x^3}\)) - (x + \(\frac{1}{x}\))
= (98 × 970) - 10 = (100 × 970) - (2 × 970) - 10 = 97000 - 1940 - 10 = 97000 - 1950 = 95050