Question

prove that bisector of any two opposite angles of a parallelogram are parallel .

Answer 1

ABCD is parallelogram..............given 
DE bisect < D, BF bisect < B..................given 
<D = <B....................opposite angles of parallelogram are equal 
<1 = <2 ................equal angle bisect still equal 
<A = <C ....................opposite angles of parallelogram are equal 
AD = BC ......................opposite sides of parallelogram are equal 
ΔADE ≅ ΔCBF...................ASA 
DE = BF..................CPCTC