Notes 7



Math 120 Notes 11.3 –The Complex Plane

I. The complex plane

A. Define: real axis, imaginary axis

1. Plot the following complex numbers

a. 3 + 3i b. -2 – i

c. -3 d. -2i

2. Let [pic] be a complex number

a. What is [pic]?

b. Find the magnitude for the complex numbers above.

3. Find a formula to convert z from rectangular to polar form, then covert the above points into polar form (degrees).

4. Plot the following polar coordinates.

a. [pic]

b. [pic]

5. Convert the polar coordinates above into rectangular form.

B. Euler’s Formula

1. Fill in the following chart:

|x |[pic] - rectangular form |[pic] - polar form |

|0 | | |

|[pic] | | |

|[pic] | | |

|[pic] | | |

|[pic] | | |

|[pic] | | |

|[pic] | | |

2. What conclusions can you make from the above analysis?

3. Convert the following into polar form

a. [pic] b. [pic]

4. Write the following in exponential form

a. [pic]

b. [pic]

III. Operations on complex numbers

A. Addition / subtraction

1. Rectangular form

a. [pic]

b. [pic]

2. Polar form: [pic] [HUH?]

B. Multiplication

1. Rectangular form: [pic]

2. Polar form

a. [pic]

b. So in general, [pic] = ?

c. Use the formula to find [pic]

3. Try multiplying [pic] by converting to polar form first.

C. Division

1. Rectangular form: [pic]

2. Polar form

a. What do you think is the formula for [pic] = ?

c. Use the formula to find [pic]

D. Power – De Moivre’s Theorem

1. Using the multiplication rule, if [pic], what is [pic], [pic], and [pic]?

2. Prove your result for [pic] using exponential notation.

3. Use De Moivre’s Theorem to write the following in standard form.

a. [pic]

b. [pic]

| |Rectangular |Polar |Exponential |

|Regular |[pic] |[pic] |- |

|Coordinates | | | |

|Complex #s |[pic] |[pic] |[pic] |

|Vectors |[pic] |[pic] |- |

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