The statement that best describes a flaw in the students' proof is;
Option D; Angle DBC and angle BDA form a pair of corresponding angles, not a pair of alternate interior angles, which are congruent.
From the given image, we can see that;
AB ≅ DC
Let us analyze each given option;
A) ∠DBC and ∠BDA are in the same triangle ΔBDC. Now, they can't be a pair of vertical angles because vertical angles are a pair of opposite angles formed when two lines intersect but this is not the case here.
They are also not alternate interior angles because alternate angles are formed when a transverse line intersects two coplanar lines and again that is not the case here.
B) In ΔABD and ΔBDC, we see that;
AB = DC. Also, by theorem of alternate interior angles, we can tell that;
∠ABD = ∠BDC
Similarly, ∠BDA = ∠DBC from alternate interior angles.
Thus, there is one corresponding side and two non-included angles which means the triangles are congruent by AAS Congruency postulate.
C) As seen in B above, this statement is correct because the triangles are congruent by AAS postulate.
D) Corresponding angles lie on the same side of the transversal. In this case, ∠BDA and ∠DBC lie on opposite sides and are even congruent by alternate interior angles.
Read more about congruency at; https://brainly.com/question/7727792
