A x y
−
=
+
với
2 2
x xy y − = 2 3
(với
x y y x y +   +  0; 0;2 3 0
).

To prove that angle def = angle dgf by sas, what additional information is needed? def congruent to dgf dfe congruent to dfg de congruent to dg dg congruent to gf