江西省2023-2024学年第一学期九年级期中质量检测数学.考卷答案

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江西省2023-2024学年第一学期九年级期中质量检测数学.考卷答案试卷答案

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分析三棱锥A-BCD中,侧棱AB、AC、AD两两相等且相互垂直,补成正方体,两者的外接球是同一个,正方体的对角线就是球的直径,由此能求出侧棱长.

解答解:三棱锥A-BCD中,侧棱AB、AC、AD两两相等且相互垂直,补成正方体,
两者的外接球是同一个,正方体的对角线就是球的直径,
设侧棱的长为a,外接球的半径为R,
∵外接球的表面积S=4π,∴4πR2=4π,
∴R=1,
∵正方体的对角线就是球的直径,
∴$\sqrt{3}$a=1,解得a=$\frac{\sqrt{3}}{3}$.
∴侧棱长为$\frac{\sqrt{3}}{3}$.

点评本题考查棱锥侧棱长的求法,是中题,解题时要认真审题,注意构造法的合理运用.