Short Notes on Complex Numbers
I.
History
1.
Quadratic and cubic equations
Solution of quadratics, solution of cubics
2.
The Fundamental Theorem of Algebra
3.
The number
i
The Fundamental Theorem of Algebra proved!
II.
Mathematics
4.
The complex plane, addition and subtraction
Notation, arithmetic operations on
C
, parallelogram rule, addition as translation, negation and subtraction
5.
Absolute value
The unit circle, the triangle inequality
6.
Multiplication
Multiplication done algebraically, multiplying a complex number by a real number, multiplication and absolute value, powers of
i,
roots of unity, multiplying a complex number by
i,
a geometric interpretation of multiplication
7.
Angles and polar coordinates
8.
Reciprocals, conjugation, and division
Reciprocals done geometrically, complex conjugates, division
9.
Powers and roots
Powers, roots, more roots of unity