Question

AB切圆O于C,AO交圆O于D,AO的延长线交圆O于E,若角A=x,角ECB=____

Answer 1

连接OC ,则有：OC⊥AB ,

可得：∠AOC = ∠OCB - ∠A = 90°- x ,

因为,OC = OE ,

所以,∠AEC = (1/2)∠AOC = 45°- (1/2)x ,

可得：∠ECB = ∠A + ∠AEC = 45°+ (1/2)x .