Chapter 9: Problem 11
Calculate the product by expressing the number in polar form and using DeMoivre's Theorem. Express your answer in the form \(a+b i\). $$\left(\frac{\sqrt{3}}{2}+\frac{1}{2} i\right)^{10}$$
Short Answer
Expert verified
Answer: The value of \(\left(\frac{\sqrt{3}}{2}+\frac{1}{2} i\right)^{10}\) is \(\frac{1}{2}-\frac{\sqrt{3}}{2} i\).
Step by step solution
01
Convert the complex number to polar form.
Given the complex number \(z=\frac{\sqrt{3}}{2}+\frac{1}{2}i\), we first need to determine its modulus and argument. The modulus (magnitude) of \(z\), denoted as \(|z|\), is given by \(|z|=\sqrt{\text{Re}(z)^{2}+\text{Im}(z)^{2}}\). In this case, \(\text{Re}(z)=\frac{\sqrt{3}}{2}\) and \(\text{Im}(z)=\frac{1}{2}\), so we have:
$$|z|=\sqrt{\left(\frac{\sqrt{3}}{2}\right)^{2}+\left(\frac{1}{2}\right)^{2}}=\sqrt{\frac{3}{4}+\frac{1}{4}}=\sqrt{1}=1$$
The argument (angle) of \(z\), denoted as \(\text{Arg}(z)\), can be found using trigonometry or by observation, considering the complex number lies in the first quadrant. In this case,
$$\text{Arg}(z)=\arctan\left(\frac{\frac{1}{2}}{\frac{\sqrt{3}}{2}}\right)=\arctan\left(\frac{\sqrt{3}}{3}\right)=\frac{\pi}{6}$$
Thus, the polar form of \(z\) is
$$z=1\left(\cos{\frac{\pi}{6}} + i\sin{\frac{\pi}{6}}\right)$$
02
Apply DeMoivre's Theorem.
Next, we want to find the value of \(z^{10}\). DeMoivre's theorem states that for a complex number in polar form \(z=r(\cos{\theta}+i\sin{\theta})\), raised to the power of \(n\), where \(n\in\mathbb{Z}\), its result can be found by multiplying the modulus by itself \(n\) times and applying the power to the angle:
$$z^n=r^n\left(\cos{(n\theta)}+i\sin{(n\theta)}\right)$$
Applying this to our complex number, which has \(n=10\), we get:
$$z^{10}=(1)^{10}\left(\cos{\left(10\frac{\pi}{6}\right)}+i\sin{\left(10\frac{\pi}{6}\right)}\right)$$
Since \((1)^{10}=1\), we have:
$$z^{10}=\cos{\frac{5\pi}{3}}+i\sin{\frac{5\pi}{3}}$$
03
Convert the result to rectangular form.
To express the result in the form \(a+bi\), we need to find the real and imaginary parts of \(z^{10}\):
$$a=\text{Re}(z^{10})=\cos{\frac{5\pi}{3}}=\frac{1}{2}$$
$$b=\text{Im}(z^{10})=\sin{\frac{5\pi}{3}}=-\frac{\sqrt{3}}{2}$$
Finally, we can write the result in rectangular form:
$$z^{10}=\frac{1}{2}-\frac{\sqrt{3}}{2} i$$
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
DeMoivre's Theorem
DeMoivre's theorem is a powerful tool in complex number theory. It allows us to easily raise complex numbers to integer powers when expressed in polar form. To apply DeMoivre’s theorem, consider a complex number written as
- \( z = r (\cos{\theta} + i \sin{\theta}) \)
- \( z^n = r^n (\cos(n\theta) + i \sin(n\theta)) \)
- polar coordinates
- magnitudes
- angles
Polar Coordinates
Polar coordinates offer a way of representing complex numbers in terms of magnitude and angle. Whereas rectangular form uses \( a + bi \), polar form uses the formula
- \( z = r (\cos{\theta} + i \sin{\theta}) \),
- Calculate the magnitude: \( r = \sqrt{a^2 + b^2} \)
- Find the angle: \( \theta = \arctan \left( \frac{b}{a} \right) \)
Rectangular Form
Rectangular form is the standard way to represent complex numbers. It uses two components:
- Real part: \( a \)
- Imaginary part: \( b \)
Trigonometry
Trigonometry plays a vital role in understanding complex numbers, especially in converting between polar and rectangular forms. It provides the mathematical foundation for transitions regarding angles and magnitudes. Key trigonometric functions involved include:
- Cosine: \( \cos \theta \) calculates the adjacent side over hypotenuse.
- Sine: \( \sin \theta \) calculates the opposite side over hypotenuse.
- Arctan: \( \arctan \theta \) helps find the angle from a ratio of two sides.