Barrons AP Calculus

x   =   r   cos θ;

y   =   r   sin θ;

r^2     =   x^2 + y^2 ;

SOME    POLAR   EQUATIONS

r   =   a circle,   center  at  pole,   radius  a.

r   =   2a  cos θ circle,   center  at  (a, 0), radius  a.

r   =   2a  sin θ circle,   center  at  (0, a), radius  a.

roses   (four   leaves)

r   =   cos 2θ.