Question 1133686
<pre>
We plot the point -4 = -4 + 0i which is the point (-4,0)

{{{drawing(200,200,-6,6,-6,6,graph(200,200,-6,6,-6,6), circle(-4,0,.2))}}}

We draw the radius vector from the origin to the point (-4,0):

{{{drawing(200,200,-6,6,-6,6,graph(200,200,-6,6,-6,6), circle(-4,0,.2),
blue(line(-4,0,0,0))
)}}}

The length of the radius vector is r = 4 units.

We indicate the counter-clockwise angle <font face="symbol">q</font> from the right side of the x-axis
around to the radius vector:

{{{drawing(200,200,-6,6,-6,6,graph(200,200,-6,6,-6,6), circle(-4,0,.2),
blue(line(-4,0,0,0)), red(arc(0,0,pi,-pi,0,180),locate(.2,2.4,theta))
)}}}

We determine from the graph that <font face="symbol">q</font> = 180°

So

{{{-4 = r(cos(theta)^""+i*sin(theta)) = 4(cos(180)^""+i*sin(180))}}}

Edwin</pre>