In Exercises 32–35, find all the complex roots. Write roots in rectangular form. The complex cube roots of −1
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- 0. Review of College Algebra4h 45m
- 1. Measuring Angles40m
- 2. Trigonometric Functions on Right Triangles2h 5m
- 3. Unit Circle1h 19m
- 4. Graphing Trigonometric Functions1h 19m
- 5. Inverse Trigonometric Functions and Basic Trigonometric Equations1h 41m
- 6. Trigonometric Identities and More Equations2h 34m
- 7. Non-Right Triangles1h 38m
- 8. Vectors2h 25m
- 9. Polar Equations2h 5m
- 10. Parametric Equations1h 6m
- 11. Graphing Complex Numbers1h 7m
11. Graphing Complex Numbers
Powers of Complex Numbers (DeMoivre's Theorem)
Problem 5.2.53
Textbook Question
In Exercises 53–64, use DeMoivre's Theorem to find the indicated power of the complex number. Write answers in rectangular form. [4(cos 15° + i sin 15°)]³
Verified step by step guidance1
Identify the complex number in polar form: \(4(\cos 15^\circ + i \sin 15^\circ)\), where the modulus \(r = 4\) and the argument \(\theta = 15^\circ\).
Recall DeMoivre's Theorem, which states that for a complex number in polar form, \((r(\cos \theta + i \sin \theta))^n = r^n (\cos n\theta + i \sin n\theta)\).
Apply DeMoivre's Theorem with \(n = 3\): compute the new modulus as \(r^3 = 4^3\) and the new argument as \(3 \times 15^\circ\).
Write the result in polar form: \(4^3 (\cos 45^\circ + i \sin 45^\circ)\).
Convert the polar form back to rectangular form using \(x = r^3 \cos 45^\circ\) and \(y = r^3 \sin 45^\circ\), so the rectangular form is \(x + iy\).
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
DeMoivre's Theorem
DeMoivre's Theorem states that for a complex number in polar form, (r(cos θ + i sin θ))^n = r^n (cos nθ + i sin nθ). It allows raising complex numbers to integer powers by multiplying the angle and raising the magnitude to the power.
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Powers Of Complex Numbers In Polar Form (DeMoivre's Theorem)
Polar and Rectangular Forms of Complex Numbers
Complex numbers can be expressed in polar form as r(cos θ + i sin θ), where r is the magnitude and θ the argument, or in rectangular form as a + bi. Converting between these forms is essential for interpreting results after applying DeMoivre's Theorem.
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Converting Complex Numbers from Polar to Rectangular Form
Trigonometric Identities for Conversion
To convert from polar to rectangular form, use a = r cos θ and b = r sin θ. Understanding these identities helps express the final answer in a + bi form after applying DeMoivre's Theorem to powers of complex numbers.
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Fundamental Trigonometric Identities
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