Perhaps we don't need to solve it by quadratic formula , juz take square root
x^2 - 12y - 36 = 0 <=>
r^2(cos^2 a) - 12r(sina) - 36 = 0 <=>
r^2[ 1 -(sin^2a)] - 12r(sina) - 36 = 0 <=>
r^2 - { [rsin(a)]^2 + 2*6[rsin(a)] + 6^2 } = 0 <=>
r^2 = [rsin(a) + 6]^2 <=>
r = rsin(a) + 6 OR r = -rsin(a) + 6
r = 6/[1 - sin(a)] OR r = 6/[ 1+ sin(a)]