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题目正三棱锥的侧面所成的二面角的平面角β的取值范围是____.(第18届(07年)“希望杯”高二2试)推广正n棱锥S—A_1A_2A_3…A_(n-1)A_n的侧面等腰三角形顶角为α,相邻两侧面所成二面角的平面角为β,则
The plane angle β of the dihedral angle formed by the side of the trigonal pyramid of the title is in the range of _____. (18th (07th)“Hope Cup” Sophomore year 2 test) Generalized n-pyramid S_A_1A_2A_3...A_ (n-1) A_n has an apex angle of the isosceles triangle at the side, and the plane angle of the dihedral angle at the adjacent two sides is β.