Math Problem Statement

Let z = z = 8 (cosine (StartFraction pi Over 3 EndFraction) + I sine (StartFraction pi Over 3 EndFraction) ) and w = 3 (cosine (StartFraction pi Over 6 EndFraction) + I sine (StartFraction pi Over 6 EndFraction) ).

Which statement describes the geometric construction of the product zw on the complex plane?

Stretch z by a factor of 3 and rotate StartFraction pi Over 2 EndFraction radians counterclockwise.

Stretch z by a factor of 3 and rotate StartFraction pi Over 6 EndFraction radians counterclockwise.

Stretch z by a factor of 24 and rotate StartFraction pi Over 2 EndFraction radians counterclockwise.

Stretch z by a factor of 24 and rotate StartFraction pi Over 6 EndFraction radians counterclockwise.

Solution

To solve this problem, we need to use the properties of multiplying complex numbers in polar form. When two complex numbers are in polar form, their product is obtained by multiplying their magnitudes and adding their angles.

Given:

  • z=8(cosπ3+isinπ3)z = 8 \left( \cos \frac{\pi}{3} + i \sin \frac{\pi}{3} \right)
  • w=3(cosπ6+isinπ6)w = 3 \left( \cos \frac{\pi}{6} + i \sin \frac{\pi}{6} \right)

Let's find the magnitude and argument of zwz \cdot w.

Step 1: Magnitude of zwzw

The magnitude of zz is z=8|z| = 8. The magnitude of ww is w=3|w| = 3.

The magnitude of the product zwzw is: zw=zw=83=24|zw| = |z| \cdot |w| = 8 \cdot 3 = 24

Step 2: Argument of zwzw

The argument of zz is arg(z)=π3\arg(z) = \frac{\pi}{3}. The argument of ww is arg(w)=π6\arg(w) = \frac{\pi}{6}.

The argument of the product zwzw is: arg(zw)=arg(z)+arg(w)=π3+π6=π2\arg(zw) = \arg(z) + \arg(w) = \frac{\pi}{3} + \frac{\pi}{6} = \frac{\pi}{2}

Conclusion

The product zwzw has a magnitude of 24 and an argument of π2\frac{\pi}{2}. Thus, on the complex plane, this transformation is represented by stretching zz by a factor of 3 and rotating by π2\frac{\pi}{2} radians counterclockwise.

Answer

The correct answer is:

  • Stretch zz by a factor of 3 and rotate π2\frac{\pi}{2} radians counterclockwise.

Would you like additional details or have any questions?


Here are five additional related questions:

  1. How would the construction change if we rotated ww by π4\frac{\pi}{4} radians instead?
  2. How can we express zwzw in rectangular form?
  3. What would happen to the construction if w|w| was doubled?
  4. How is the rotation angle affected if the angle of zz changes?
  5. Can we interpret the rotation direction (counterclockwise) in terms of the unit circle?

Tip: When multiplying complex numbers in polar form, always remember to multiply the magnitudes and add the angles for an efficient solution.

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Math Problem Analysis

Mathematical Concepts

Complex Numbers
Polar Coordinates
Multiplication of Complex Numbers

Formulas

Magnitude of product: |zw| = |z| * |w|
Argument of product: arg(zw) = arg(z) + arg(w)

Theorems

Multiplication of complex numbers in polar form

Suitable Grade Level

Grades 11-12