ABCDE是半径为R的圆内接正五边形,P为弧AE的中点,求PA乘PB=r的平方
问题描述：
ABCDE是半径为R的圆内接正五边形,P为弧AE的中点,求PA乘PB=r的平方
答
连接OP,OA,OBPOB中PB/sin(POB)=PO/sin(PBO)PB/sin(108°)=R/sin(36°)POA中PA/sin(POA)=PO/sin(PAO)PA/sin(36°)=R/sin(72°)PB/sin(108°) * PA/sin(36°)=R/sin(36°) * R/sin(72°)sin(108°)=sin(180°-108°)=s...