DE垂直平分斜边AB,分别交AB,AC于D,E
则:AE=EB,
角EAB=角B,
角CAE+角EAB+角B=90
则可求:角CAE=90-2角B
又:角CAE=角B+30度
则:角B=20,
角EAB=20
角AEB=180-20*2=140