13. In isosceles triangle HMS, ZM is the vertex angle. If m2M = (2x + 6)° and mZH (9x + 7)º, what
is mZM?
A. 10°
B. 22°
C. 79°
D. 80°

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.