在直角梯形ABCD中,AB平行于DC,AB垂直于BC,角A等于60度,AB等于2CD,E F分别为AB AD中点,连接EF EC BF CF

CD=AE CD//AE =>AD//CE =>四边形AECD 是平行四边形.
=>三角形CDE全等于三角形AED
BE=CD BE//CD =>DE//BC =>BC垂直AB=>DE垂直AB
CD=2 =>AE=2 =AF=FD
AD=4 DE=2根号3
S三角形AEF=S三角形AED/2=(2*2根号3/2)/2=根号3
S三角形CDF=(CD*DF*sinD)/2=根号3
四边形BCFE面积=梯形ABCD面积-S三角形AEF-S三角形CDF
=(2+4)*2根号3/2-2根号3=4根号3