Which of these is a function?
{(0, 4), (0, 5), (0, 9), (0, 23)}
{(0, 1), (1, 2), (1, 5), (2, 9)}
{(0, 4), (2, 4), (3, 7), (4, 9)}
{(6, 0), (6, 1), (6, 7), (6, 11)}

Given: ae ≅ ce ; de ≅ be prove: abcd is a parallelogram. we have that ab || dc. by a similar argument used to prove that △aeb ≅ △ced, we can show that △ ≅ △ceb by. so, ∠cad ≅ ∠ by cpctc. therefore, ad || bc by the converse of the theorem. since both pair of opposite sides are parallel, quadrilateral abcd is a parallelogram.