means side , which is opposite to angle , is shorter than side , which is opposite to the larger angle . But . Hence:
:A similar construction shows , establishing the theorem.

An alternative proof (also based upon the triangle postulate) proceeds by considering three positions for point : (i) as depicted (which is to be proved), or (ii) coincident with (which would mean the isosceles triangle had two right angles as base angles plus the vertex angle , which would violate the triangle postulate),