Vertices A,B,C of a equilateral triangle of side 1 are in the surface of a sphere with radius 1 and center O. Let D be the orthogonal projection of A on the plane α determined by points B,C,O. Let N be one of the intersections of the line perpendicular to α passing through O with the sphere. Find the angle ∠DNO. geometry3D geometrySpaintrigonometry