Practicing Success
If x2 - 4x + 1 = 0 find x9 + x7 - 194x5 - 194x3 |
4 2\(\sqrt {3}\) -4 -2\(\sqrt {3}\) |
-4 |
x2 - 4x + 1 = 0 ⇒ x + \(\frac{1}{x}\) = 4 If x + \(\frac{1}{x}\) = 4 x2 + \(\frac{1}{x^2}\) = x2 - 2 ⇒ x2 + \(\frac{1}{x^2}\) = 14 ⇒ x4 + \(\frac{1}{x^4}\) = 196 Put in find ⇒ x9 + x7 - (x4 + \(\frac{1}{x^4}\))x5 - (x4 + \(\frac{1}{x^4}\))x3 ⇒ x9 + x7 - x9 - x - x7 - \(\frac{1}{x}\) -x - \(\frac{1}{x}\) = -\(\left(x+\frac{1}{x}\right)\) = -4 |