JEE Advance - Mathematics (1987 - No. 19)
A polygon of nine sides, each of length $$2$$, is inscribed in a circle. The radius of the circle is .................
$$\sin ec\,\frac{\pi}{9}$$
$$\cos ec\,\frac{\pi}{18}$$
$$\cos ec\,\frac{\pi}{9}$$
$$\sin \,\frac{\pi}{9}$$
$$\cos \,\frac{\pi}{9}$$