M为OB的中点,CM的延长线交圆O于点E,且EM大于MC,连结DE,DE=根号15。SIN角EOB的值。
连接AE,
cosD=DE/2R=15^0.5/8
sin²D=1-cos²D=1-15/64=49/64
sinD=7/8
AO=EO,所以∠A=∠AEO
因为∠EOB=∠EAO+∠AEO(外角等于两对角和)
∠EOB=2*∠EAO
sinEOB=sin2EAO=sin2D(EAO=∠D,因两角所对弧相等)
sinEOB=sin2D=2sinD*cosD=2*7/8*15^0.5/8
=7*15^0.5/32=0.85