Hello,

If the polar coordinate is defined as:

x=r cos(theta)

y=r sin(theta)

then,

r=\sqrt{x^2+y^2},

cos(theta)=x/r,

sin(theta)=y/r.

By substituton,

r=-3 cos(theta) becomes

r=-3x/r that is, r^2=-3x

so that x^2+y^2=-3x.

((x+3/2)^2+y^2=(3/2)^2.)

Please adjust the above argument to the appropriate polar coordinate you are using...

Bye.