Hi have a question which requires changing polar coordiantes to cartesian for the equation r=exp(titah)

using

r = (sqrt(x^2+y^2)

titah = arctan(y/x)

r = x/cos(titah) = y/sin(titah)

i get this equation

sqrt(x^2+y^2) = exp(arctan(x/y)

ln(sqrt(x^2+y^2)=arctan(x/y)

any help on how to separate the variables? to form an equation y=f(x)