When is csc theta = 0?
Here is the graph for y=csc(x)
You can see that y=0 is an asymptote
If csc(θ) = a/b, then sin(θ) = b/a.
Since csc(θ) = 0, then csc(θ) = 0/1 ---> sin(θ) = 1/0 (which is undefined)
So csc(θ) can't equal 0.