ABCD是梯形,
过A作AE平行DC交BC于E,
AECD是平行四边形,
EC=AD=3,AE=DC=4,
BE=BC-EC=3,
三角形ABE中,BE=3,AB=5,AE=4,
角AEB=90度,
AE是梯形ABCD的高,
S四边形ABCD
=(AD+BC)*AE/2=18
ABCD是梯形,
过A作AE平行DC交BC于E,
AECD是平行四边形,
EC=AD=3,AE=DC=4,
BE=BC-EC=3,
三角形ABE中,BE=3,AB=5,AE=4,
角AEB=90度,
AE是梯形ABCD的高,
S四边形ABCD
=(AD+BC)*AE/2=18