MathDB

In quadrilateral

ABCD

E

and

F

are midpoints of

AB

and

CD

, and

G

is the intersection of

AD

with

BC

P

is a point within the quadrilateral, such that

PA=PB

PC=PD

, and

\angle APB+\angle CPD=180^{\circ}

. Prove that

PG

and

EF

are parallel.

P3