Given and , find the product .
Table of contents
- 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
Products and Quotients of Complex Numbers
Problem 37
Textbook Question
In Exercises 37–44, find the product of the complex numbers. Leave answers in polar form. z₁ = 6(cos 20° + i sin 20°) z₂ = 5(cos 50° + i sin 50°)
Verified step by step guidance1
Recall that when multiplying two complex numbers in polar form, the magnitudes multiply and the angles add. This is based on De Moivre's Theorem.
Identify the magnitudes and angles of the given complex numbers: For \(z_1 = 6(\cos 20^\circ + i \sin 20^\circ)\), the magnitude is 6 and the angle is \(20^\circ\). For \(z_2 = 5(\cos 50^\circ + i \sin 50^\circ)\), the magnitude is 5 and the angle is \(50^\circ\).
Multiply the magnitudes: \(r = 6 \times 5\).
Add the angles: \(\theta = 20^\circ + 50^\circ\).
Write the product in polar form as \(r(\cos \theta + i \sin \theta)\) using the values found in steps 3 and 4.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Polar Form of Complex Numbers
A complex number can be expressed in polar form as r(cos θ + i sin θ), where r is the magnitude (modulus) and θ is the argument (angle). This form is useful for multiplication and division because it separates the magnitude and angle components.
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Multiplication of Complex Numbers in Polar Form
When multiplying two complex numbers in polar form, multiply their magnitudes and add their angles. Specifically, if z₁ = r₁(cos θ₁ + i sin θ₁) and z₂ = r₂(cos θ₂ + i sin θ₂), then z₁z₂ = r₁r₂ [cos(θ₁ + θ₂) + i sin(θ₁ + θ₂)].
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De Moivre's Theorem
De Moivre's theorem states that raising a complex number in polar form to a power n results in rⁿ [cos(nθ) + i sin(nθ)]. While not directly required here, it underpins the manipulation of angles and magnitudes in polar form and helps understand multiplication as repeated addition of angles.
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