I assume you mean, that an angle and two sides are known.
A formula that can be used for irregular triangles is the cosine rule.
[tex]a = {b}^{2} + {c}^{2} - 2ab \cos(angle \: opposite \: a) [/tex]
'b' and 'c' must be sides that are beside the angle 'A' (angle opposite 'a').
