3 -
i
This is the vector from the origin (0,0) to point
.
It has length r, which is always a positive number.
So we draw the vector:
Then we draw the perpendicular to the x-axis:
Then the green line is the same as the y-coordinate
,
negative because it goes down from the x-axis. and the horizontal
line from the origin to the green line is the x-coordinate 3.
We calculate r which is the length of the vector by the Pythagorean
theorem:
r² = x² + y²
r² = 3² + (
)²
r² = 9 + 3
r² = 12
r =
r =
r =
Next we calculate
, which is the angle from
the right side of the x-axis to the vector, as indicated
by the red arc below:
First we calculate the reference angle, indicated by the blue arc, the
smallest angle between the vector and the x-axis:
We can calculate it using any trig function, let's pick the sine:
sin(reference angle) =
=
So the reference angle is 30° and therefore
= 360° - 30° = 330°
So the trig form (or polar form) of the complex number
3 -
i
is
r(cos
+ i·sin
) or
2
[cos(330°) + i·sin(330°)]
Edwin