设a1a2a3a4a5a6a7是圆内接正七边形,求证:1/a1a2=1/a1a3 1/a1a4 .

设a1a2a3.a7是圆内接正七边形,求证:1/(a1a2)等于1/(a1a3) 1/(a1a4)

谢谢,求图中正八边形内角度数.