Let ABCD BE A QUADRILATERAL WHOSE DIAGONALS ARE 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 .
.