### Video Summary:

Call the horizontal axis the real axis and the vertical axis the imaginary axis. Now complex numbers can be graphed in this complex plane. The sum of two complex numbers can be represented graphically by the vector that is the resultant of the sum of vectors corresponding to the two numbers.
Trigonometric or Polar Form of a Complex Number
The expression
r(cos + i sin ) Notation:
cos + i sin is sometimes written cis . Using this notation, r(cos + i sin ) is written r cis .
The number r is called the modulus or absolute value of the complex number x + yi.
Angle is called the argument of the complex number x + yi.