AB=30BE+AE=40根据勾股定理AB^2+BE^2=AE^2所以BE=8.75AE=31.25sin(角AEB)=(30/31.25)所以角AEB=73.74度角AEF+角AEB+角FEC=180角AEF=角FEC所以角AEF=53.13连接AFAE=EF所以角AEF=角AFE所以角AFE=53.13所以角FAE=73.74根据正弦定理sin73.74/EF=sin53.13/31.25所以EF=37.5