Quadratic And Proof
1. **State the problems:**
Solve the quadratic equation $9x^2 - 3x + 1 = 0$ and then prove that $$81\left(x^4 + \frac{1}{6561x^4}\right) = 1.$$
2. **Solve the quadratic equation:**
Given: $$9x^2 - 3x + 1 = 0.$$
Use the quadratic formula: $$x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a},$$ where $a=9$, $b=-3$, $c=1$.
Calculate the discriminant:
$$\Delta = (-3)^2 - 4 \times 9 \times 1 = 9 - 36 = -27.$$
Since the discriminant is negative, the roots are complex:
$$x = \frac{3 \pm \sqrt{-27}}{18} = \frac{3 \pm 3i\sqrt{3}}{18} = \frac{1 \pm i\sqrt{3}}{6}.$$
3. **Calculate $x^4$:**
Let $x = \frac{1 + i\sqrt{3}}{6}$ (the process will be similar for the conjugate).
First find $6x = 1 + i\sqrt{3}$.
Note that $1 + i\sqrt{3} = 2\left(\frac{1}{2} + i \frac{\sqrt{3}}{2}\right) = 2 e^{i \pi/3}$.
Then,
$$ (6x)^4 = (2 e^{i \pi/3})^4 = 2^4 e^{i 4\pi/3} = 16 e^{i 4\pi/3}.$$
Consequently,
$$ x^4 = \frac{(6x)^4}{6^4} = \frac{16 e^{i 4\pi/3}}{1296} = \frac{16}{1296} e^{i 4\pi/3} = \frac{1}{81} e^{i 4\pi/3}.$$
4. **Calculate $\frac{1}{6561 x^4}$:**
Since $6561 = 81^2$, we get
$$ \frac{1}{6561 x^4} = \frac{1}{81^2 x^4} = \frac{1}{81^2} \cdot \frac{1}{x^4} = \frac{1}{81^2} \cdot \frac{1}{\frac{1}{81} e^{i 4\pi/3}} = \frac{1}{81} e^{-i 4\pi/3}.$$
5. **Add $x^4$ and $\frac{1}{6561 x^4}$:**
$$x^4 + \frac{1}{6561 x^4} = \frac{1}{81} e^{i 4\pi/3} + \frac{1}{81} e^{-i 4\pi/3} = \frac{1}{81} \left(e^{i 4\pi/3} + e^{-i 4\pi/3}\right).$$
Recall that $e^{i\theta} + e^{-i\theta} = 2 \cos \theta$, so:
$$x^4 + \frac{1}{6561 x^4} = \frac{2}{81} \cos \left( \frac{4\pi}{3} \right).$$
6. **Evaluate $\cos(4\pi/3)$:**
$$\cos \left( \frac{4\pi}{3} \right) = \cos \left( \pi + \frac{\pi}{3} \right) = -\cos \left( \frac{\pi}{3} \right) = - \frac{1}{2}.$$
7. **Plug the cosine value back:**
$$x^4 + \frac{1}{6561 x^4} = \frac{2}{81} \times \left(- \frac{1}{2}\right) = - \frac{1}{81}.$$
8. **Multiply both sides by 81:**
$$81 \left(x^4 + \frac{1}{6561 x^4} \right) = 81 \times \left(- \frac{1}{81} \right) = -1.$$
**However, the problem states to prove this equals 1, but our calculation gives -1.**
9. **Explanation:**
The value is $-1$ given the roots and calculations above.
Possibly the problem expects a slightly different expression or there might be a typo.
**Final solution:**
The quadratic solutions are $$x = \frac{1 \pm i\sqrt{3}}{6}.$$ The value of $$81\left(x^4 + \frac{1}{6561x^4}\right) = -1,$$ not 1.