For what values of θ is the tangent 0?
for what values of θ is the tangent undefined?
explain

Tangent is actually the ratio of sine to cosine.
TanФ = sinФ/cosФ
Therefore, tangent becomes 0 when sin is 0; i.e at intervals of nπ(n is any integer starting from 0) and becomes undefined when cos is 0; i.e at intervals of nπ(n is any odd integer starting from 1).