Circle S is shown. Line segment R T is a diameter. The length of S T is 4. Sector R S T is shaded. The measure of central angle RST is radians. What is the area of the shaded sector? 4Pi units squared 8Pi units squared 16Pi units squared 20Pi units squared

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.