JEE MAIN - Mathematics (2023 - 13th April Evening Shift - No. 8)
Explanation
Find the roots of the quadratic equation:
The quadratic formula is $$x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$$. For the quadratic equation $$x^2 - \sqrt{2}x + 2 = 0$$, we have $$a = 1, b = -\sqrt{2}, c = 2$$. Plugging these into the quadratic formula gives:
$$x = \frac{\sqrt{2} \pm \sqrt{(-\sqrt{2})^2 - 4(1)(2)}}{2(1)} = \frac{\sqrt{2} \pm \sqrt{2 - 8}}{2} = \frac{\sqrt{2} \pm \sqrt{6}i}{2}.$$
So, we have two roots, $\alpha$ and $\beta$, which are:
$$\alpha = \frac{\sqrt{2} + \sqrt{6}i}{2},$$
$$\beta = \frac{\sqrt{2} - \sqrt{6}i}{2}.$$Express the roots in exponential form:
We can express complex numbers in the form $$re^{i\theta}$$. For $\alpha$ and $\beta$, we find the magnitude $$r = \sqrt{2}$$ and the arguments $$\theta = \frac{\pi}{3}, -\frac{\pi}{3}$$ respectively. So, we have:
$$\alpha = \sqrt{2}e^{i\frac{\pi}{3}},$$
$$\beta = \sqrt{2}e^{-i\frac{\pi}{3}}.$$Calculate the 14th power of the roots:
To find $$\alpha^{14}$$ and $$\beta^{14}$$, we use the property of exponents which says that $$(a^m)^n = a^{mn}$$. So, we have:
$$\alpha^{14} = (\sqrt{2}e^{i\frac{\pi}{3}})^{14} = 2^7e^{i\frac{14\pi}{3}} = 128e^{i\frac{2\pi}{3}},$$
$$\beta^{14} = (\sqrt{2}e^{-i\frac{\pi}{3}})^{14} = 2^7e^{-i\frac{14\pi}{3}} = 128e^{-i\frac{2\pi}{3}}.$$Add the 14th powers of the roots:
We want to find the real part of $$\alpha^{14} + \beta^{14}$$. To do this, we use the property that $$e^{ix} = \cos(x) + i\sin(x)$$. We have:
$$\alpha^{14} + \beta^{14} = 128e^{i\frac{2\pi}{3}} + 128e^{-i\frac{2\pi}{3}} = 128(2)\cos\left(\frac{2\pi}{3}\right) = -128.$$
Comments (0)
