The shape and size of a <a href="https://en.wikipedia.org/wiki/triangle" class="extiw" title="w:triangle">triangle</a> can be uniquely determined up to <a href="https://en.wikipedia.org/wiki/congruence_(geometry)" class="extiw" title="w:congruence (geometry)">congruence</a> by specifying the lengths of two sides and the angle between them (SAS) or two angles and the side between them (ASA).  Specifying two angles and an adjacent side (AAS) also works, but specifying two sides and an adjacent angle (SSA) usually gives two different possible solutions. This is called the <i>ambiguous case</i>.
<a href="//commons.wikimedia.org/wiki/User:Ilmari_Karonen" title="User:Ilmari Karonen">Ilmari Karonen</a>
<span class="int-own-work" lang="en">Own work</span>