In polar coordinates, why asymptote means r=infinity? As stated in here: https://math.stackexchange.com/questions/100665/horizontal-and-vertical-asymptotes-of-polar-curve-r-theta-pi-theta, the first line in Answer: "An asymptote is going to mean that , which happens when the denominator approaches zero."

I don't need to answer the problem in the link, I only need a proof why when it means an asymptote in polar coordinates.