SOLUTION: Sketch a graph of the polar equation, and express the equation in rectangular coordinates. θ=-pi/2

This is one that you can't use the usual formulas 
to convert with.  You must understand how 
polar graphs work.  I'll show you what you must
do when the formulas won't work:

There is no "r" in this equation, however
you could think of it as having the term 0r,
like this



Then you can get a few polar points

 r | θ
---------
 1 | -π/2    (r,θ) = (1,-π/2)  
 2 | -π/2    (r,θ) = (2,-π/2) 
 3 | -π/2    (r,θ) = (3,-π/2) 
-1 | -π/2    (r,θ) = (-1,-π/2) 
-2 | -π/2    (r,θ) = (-2,-π/2) 
-3 | -π/2    (r,θ) = (-3,-π/2) 

The polar point (r,θ) means to swing a radius line around through the
angle θ, counter-clockwise if θ is positive and clockwise if
θ is negative.  Then go out on that radius line as many units as 
the value of r in that direction.  If the value of r is 
positive, you go out away from the origin (or pole).  If the
value of r is negative you go backward through the origin
or pole.

Using polar graph "spider-web" paper, this is how you plot the 
polar point (r,θ) = (2,-π/2).

Starting for the "east" (right side of the horizontal, 
swing around through π/2 radians or 90° CLOCKWISE 
since θ is NEGATIVE, indicated by the red arc,
then go out 2 units, along the red line, and plot a point.
Normally we don't show the red arc or the red line to keep
from cluttering up the graph, but I'll do it for this 
illustration:
 

  
----
Using polar graph paper, this is how you plot the polar point
(r,θ) = (-3,-π/2).

Starting again for the "east" (right side of the horizontal, 
swing around as before through π/2 radians or 90° CLOCKWISE 
since θ is NEGATIVE, indicated by the red arc,
but this time how you go out is different.  You go out 3 units, 
but this time BACKWARDS through the origin along the red line, 
which goes BACKWARDS through the origin and plot a point.  That's
because the value of r is NEGATIVE.  Like this:


 
When all the points are plotted we have this:
and when we connect all those points we have this vertical 
line:



Now if we superimpose rectangular graph paper
on the "spider-web" graph paper, we get this:



As you see, the graph is the line which is the y-axis.
And the rectangular equation of the y-axis is 

x = 0      <-- that's the rectangular equation for 

If you need to ask me any questions about this, feel free 
to ask them in the thank-you note form below.  I'll get back
to you by email.  (no charge ever. I do this as a hobby).

Edwin