Answer:
According to theorem 7.5
Î ABB'A' ≅ Î DEE'D' Â
therefore by transitivity of equivalence  it is proven that triangle ABC and triangle DEF are triangles with equal defects and a pair of congruent sides
Step-by-step explanation:
To prove that triangle ABC and triangle DEF are triangles with equal defects and a pair of congruent sides :
Assume:  б(Δ ABC ) =  б(Δ DEF ) and also AB ≅ DE
let ΠABB'A' and DEE'D' be taken as the saccheri quadrilaterals that corresponds to Δ ABC and Δ DEF  respectively
Following the Lemma above; б(ΠABB'A' ) = б( ΠDEE'D' ) given that
AB = summit of ABB'A' and DE = summit of DEE'D'  also  AB ≅ DE
According to theorem 7.5
Î ABB'A' ≅ Î DEE'D' Â
therefore by transitivity of equivalence  it is proven that triangle ABC and triangle DEF are triangles with equal defects and a pair of congruent sides