well? since tan90 is undefined as well is sec90... how does cot90=0
Draw several right triangles with one angle 90 degrees (of course) and another angle close to 90 degrees, keeping the hypotenuse of constant length. is "near side over hypotenuse". As approaches 90 degrees, the "near" gets shorter and shorter: goes to 0.
As to your refernce to tangent and secant: both of those have cosine in the [b]denominator[b] while the numerator is 1: in a limiting sense, 1/0= infinity.