When a function/expression is "undefined", their denominator would equal to zero.
When would f(x)=1/0? When x=0!
Therefore, when x=0, the function would become undefined.
If you have a more complex function such as 1/2x+3 and you want to find the point it becomes undefined,
Make 2x+3=0 and find x.
2x+3=0
2x=-3
x=-3/2 (at this point it becomes undefined)
Hope I helped :)
