To convert a Polar Eqn. r=f(θ) into a Rectangular one y=F(x), we need the following Conversion Formulae :
cosθ=xr,sinθ=yr,r2=x2+y2
Hence, the given polar eqn. r=6 becomes, √x2+y2=6,i.e.,
x2+y2=36, which is the eqn. of a Circle having Centre at the
Origin O(0,0) and radius 6.