- Prooffollowsthe lessonexampleclosely. Assume is even.Thenit can be shownthat mustbe
even,whichis a contradiction. - In we have. Assumethat is a right angle.Hence,by
substitutionwe have so that , whichis a contradiction.
- Supposewe havea trianglein whichthe sidesoppositetwo anglesare congruent.Thenit followsthat
the trianglemustbe isosceles.By IsoscelesTriangleTheorem,the oppositeanglesare congruent,which
is a contradiction. - Assume doesbisect. Hence,the two trianglesare congruentby SAS and
by CPCTC,whichis a contradiction.