1.连BE∵AB=A'B,BE=BE∴Rt△ABE≌Rt△A'BE∴AE=A'E2.同理A'F=CF=y∴DE=1-x,DF=1-y,EF=x+y(1-x)²+(1-y)²=(x+y)²y=(1-x)/(1+x)3.有可能△EFD为等腰直角三角形时∠DEF=45°∴∠A'BC=45°∴α=45°BCmax=...