CK-12 Geometry-Concepts

6.4. Quadrilaterals that are Parallelograms http://www.ck12.org

14.

For questions 15-17, determine ifABCDis a parallelogram.

15.A( 8 ,− 1 ),B( 6 , 5 ),C(− 7 , 2 ),D(− 5 ,− 4 )

16.A(− 5 , 8 ),B(− 2 , 9 ),C( 3 , 4 ),D( 0 , 3 )

17.A(− 2 , 6 ),B( 4 ,− 4 ),C( 13 ,− 7 ),D( 4 ,− 10 )

Write a two-column proof.

18.Parallelogram Diagonals Theorem Converse

Given:AE∼=EC,DE∼=EBProve:ABCDis a parallelogram

19.

Given:^6 ADB∼=CBD,AD∼=BCProve:ABCDis a parallelogram

Suppose thatA(− 2 , 3 ),B( 3 , 3 )andC( 1 ,− 3 )are three of four vertices of a parallelogram.