If x + \(\frac{1}{x}\) = 4
Find x5 + \(\frac{1}{x^5}\)
Answer & explanation
Correct answer: option 4
Formula → [x5 + \(\frac{1}{x^5}\) = (x3 + \(\frac{1}{x^3}\)) (x2 + \(\frac{1}{x^2}\)) - (x + \(\frac{1}{x}\))]
→ [x2 + \(\frac{1}{x^2}\) = a2 - 2 If x + \(\frac{1}{x}\) = a]
→ [x3 + \(\frac{1}{x^3}\) = a3 - 3a]
x + \(\frac{1}{x}\) = 4
x2 + \(\frac{1}{x^2}\) = 42 - 2 = 14
x3 + \(\frac{1}{x^3}\) = (4)3 - 3 × 4 = 52
Now; x5 + \(\frac{1}{x^5}\) = 52 × 14 - 4 = 724