Let ABCD BE A QUADRILATERAL WHOSE DIAGONALS R AC AND BD ABD O ANY POINT WITHIN QUADRILATERAL .

JOIN O WITH A,B,C,D

IN ACO

OA+OC > A.C. ...... ( 1 )

( IN triangle sum of 2 SIDESGREATER than 3rd sides )

similarly in BOD

OB+OD > BD......... (2)

ADDING BOTH EQUATION WE GET

OA+OC +OB+OD> AC+ BD .

HOPE IT HELP YOU