Question

已知四边形ABCD各顶点的坐标分别是A(0,0)B(3,6),C(4,8),D(6,0)求四边形ABCD的面积

Answer 1

过B作BE垂直于AD,过C作CF垂直于AD.

那么有:AE=3,AF=4,EF=1,BE=6,CF=8,FD=2

S(ABCD)=S(ABE)+S(BEFC)+S(CFD)

=1/2AE*BE+(BE+CF)*EF/2+1/2FD*CF

=1/2*3*6+(6+8)*1/2+1/2*2*8

=9+7+8

=24