
2-1 (a) Polar coordinates and the Argand plane
Point 1 of 8 — Lesson 1: Complex Numbers in Trigonometric and Exponential Form and De Moivres TheoremQuestion bank: 6 questions (1 with pictures)
01 2-1 (a) Polar coordinates and the Argand plane
Polar and Cartesian coordinates
- A point at distance from the origin, with the radius making angle with the positive -axis, has polar coordinates .
- Polar axis: the positive part of the -axis, from which the angle is measured.
- Polar to Cartesian:
- Cartesian to polar:
- So the Cartesian point can be written as .
Argand plane
- Argand plane (Argand diagram): a Cartesian plane in which the -axis is the real axis and the -axis is the imaginary axis.
- The complex number is represented by the point (or by the vector from the origin to that point).
- Jean-Robert Argand was the first to study complex numbers in detail; he used them to show that every algebraic equation has roots, real or imaginary.
Symmetry on the Argand plane
- The points representing and are symmetric about the origin.
- The points representing and its conjugate are symmetric about the real axis (-axis).
- The point representing is the fourth vertex of the parallelogram built on the vectors of and .
- Example: and are symmetric about ; and are symmetric about the real axis.
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