AB = CD, BC AD prove that triangle ABC is equal to triangle ACD.

Given AB = CD, BC = AD. To prove the equality of triangle ABC and triangle ACD, you need to select three features in order to identify the feature. Our two sides are pairwise equal, and the third – AC – is common, this fits the formulation of the third criterion for the equality of triangles. It sounds like this: if the three sides of one triangle are equal respectively to the three sides of the other triangle, then such triangles are equal. AB = CD, BC = AD, AC – general => triangle ABC is equal to triangle ACD, as required.