S△ADB=S△DAC(同底等高) 各减 S△AOD=1
=> S△COD=S△AOB=4
S△COD:S△AOD=CO:OA=S△BOC:S△AOB=4:1=S△BOC:4 =>S△BOC=16
so S[ABCD]=1+4+4+16=25