How could you change r=-3sin(Theta) into a rectangular equation?
Call t = theta.
x = r*cos(t)
y = r*sin(t)
So
r = sqrt{x^2 + y^2}
Now, sin(t) = y/r = y/sqrt{x^2 + y^2}
Thus:
r = -3*sin(t) <==> sqrt{x^2 + y^2} = -3*y/sqrt{x^2 + y^2}
Now simplify until you have a form that satisfies you.
-Dan
(If you mulitply both sides by sqrt{x^2 + y^2} it starts looking suspisciously like a circle. See if you can prove that.)