Euclid's Elements-Book I-Proposition 25

If two triangles have the two sides equal to two sides respectively, but have the base greater than the base, they will also have the one of the angles contained by the equal straight lines greater than the other.
In other words...
Suppose two triangles have two congruent sides respectively, but the base of one triangle is longer than the other. The triangle with the longer base will also have a greater angle measure included between the two congruent sides.
1. Construct triangle ABC. [br]2. Construct segment DE such that AB=DE,[br]3. Construct segment DF such that AC=DF.[br]4. Connect points E and F.[br][br][br][br][br][br][br][br][br][br]
– Inshirah Barakat-Romman

Information: Euclid's Elements-Book I-Proposition 25