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kirill115 [55]
3 years ago
13

Precal help if you could could you answer both. Me finishing this helps me graduate.

Mathematics
1 answer:
oee [108]3 years ago
7 0

Exercise 1:

The easiest way to compute powers of complex numbers is to write them in the form

z = \rho e^{i\theta} = \rho(\cos(\theta)+i\sin(\theta))

In this form, you have

z^n = \rho^n e^{in\theta} = \rho^n(\cos(n\theta)+i\sin(n\theta))

The magnitude of the number is given by

z=a+bi \implies \rho = \sqrt{a^2+b^2}

So, we have

z=-1+\sqrt{3}i \implies \rho = \sqrt{1+3}=2

As for the angle, we have

z=a+bi \implies \theta = \text{atan2}\dfrac{b}{a}

So, we have

z=-1+\sqrt{3}i \implies \theta = \text{atan2}\left(\dfrac{-\sqrt{3}}{-1}\right) = -\dfrac{2\pi}{3}

Finally,

z=-1-\sqrt{3}i = 2\left(\cos\left( -\dfrac{2\pi}{3}\right) + i\sin\left( -\dfrac{2\pi}{3}\right)\right) \implies z^6 = 2^6\left(\cos\left( -4\pi\right) + i\sin\left(-4\pi\right)\right) = 64

Exercise 2:

You simply have to compute the trigonometric function:

\cos\left(-\dfrac{\pi}{4}\right) = \dfrac{\sqrt{2}}{2},\quad \sin\left(-\dfrac{\pi}{4}\right) = -\dfrac{\sqrt{2}}{2}

So, we have

z = \sqrt{2}\left(\dfrac{\sqrt{2}}{2} - i\dfrac{\sqrt{2}}{2}\right) = 1-i

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