1、设四边形ABCD,AB=4.4,BC=8.2,CD=3.8,AD=8.9,这里A和C都可能是90度,选A是直角,
S△ABD=8.9*4.4/2=19.58,
BD=9.928
S△BCD=√（10.964*1.036*7.164*2.764)
=14.997,
S四边形ABCD=19.58+14.997=34.577.
2、设四边形ABCD
AB=3.37,BC=9.79,CD=3.76,AD=8.55,
选A是直角,
S△ABD=3.37*8.55/2=14.4067
BD=√84.4194=9.1902
S△BCD=√11.37*2.18*1.58*7.61
=17.2635
S四边形ABCD=14.4067+17.2635=31.67
3、设四边形ABCD
AB=3.12,BC=7,CD=3.8,AD=7.5,
仍设A角为90度,
S△ABD=7.5*3.12/2=11.7
BD=8.1231,
S△BCD=√9.061*0.9384*2.0615*6.0615
=10.3077
S四边形ABCD=11.7+10.3077=22.01.