(本小题满分 13 分) 图5所示的几何体是将高为 2,底…——2011 高考数学第 17 题答案解析

2011_退役省自主命题 (2011·文)

2011 ?? 第 17 题 解答题 区分题
2011_退役省自主命题 (2011·文)

18.(本小题满分 13 分)
图5所示的几何体是将高为 2 ,底面半径为 1 的直圆柱沿过轴的平面切开后,将其中一半沿切面向右水平平移后得到的.$A, A^{\prime}, B, B^{\prime}$ 分别为 $\overparen{C D}, \overparen{C^{\prime} D^{\prime}}, \overparen{D E}, \overparen{D^{\prime} E^{\prime}}$ 的中点,$O_{1}, O_{1}^{\prime}, O_{2}, O_{2}^{\prime}$ 分别为 $C D, C^{\prime} D^{\prime}$ , $D E, D^{\prime} E^{\prime}$ 的中点.
(1)证明:$O_{1}^{\prime}, A^{\prime}, O_{2}, B$ 四点共面;

(2)设 $G$ 为 $A A^{\prime}$ 中点,延长 $A^{\prime} O_{1}^{\prime}$ 到 $H^{\prime}$ ,使得 $O_{1}^{\prime} H^{\prime}=A^{\prime} O_{1}^{\prime}$ .证明:$B O_{2}^{\prime} \perp$ 平面 $H^{\prime} B^{\prime} G$


图5

完整解析 · 逐步详解

【解析】证明:(1)连接 $\mathrm{BO}_{2}, \mathrm{O}_{2} \mathrm{O}_{2}{ }^{\prime}$ ,
依题意得 $O_{1}, O_{1}^{\prime}, O_{2}, O_{2}^{\prime}$ 是圆柱底面圆的圆心
$\therefore C D, C^{\prime} D^{\prime}, D E, D^{\prime} E^{\prime}$ 是圆柱底面圆的直径
$\because A^{\prime}, B, B^{\prime}$ 分别为 $\widehat{C^{\prime} D^{\prime}}, \widehat{D E}, \widehat{D^{\prime} E^{\prime}}$ 的中点
$\therefore \angle A^{\prime} O_{1}^{\prime} D^{\prime}=\angle B^{\prime} O_{2}^{\prime} D^{\prime}=90^{\circ}$
$\therefore A^{\prime} O_{1}^{\prime} / / B O_{2}^{\prime}$
$\because B B^{\prime} / / O_{2} O_{2}{ }^{\prime}$ ,四边形 $O_{2} O_{2}{ }^{\prime} B^{\prime} B$ 是平行四边形
$\therefore B O_{2} / / B O_{2}{ }^{\prime}$
$\therefore A^{\prime} O_{1}^{\prime} / / B O_{2}$
$\therefore O_{1}^{\prime}, A^{\prime}, O_{2}, B$ 四点共面
(2)延长 $A^{\prime} O_{1}$ 到 $H$ ,使得 $O_{1}^{\prime} H=A O_{1}^{\prime}$ ,连接 $H H^{\prime}, H O_{1}^{\prime}, H B$

$\because O_{1}^{\prime} H^{\prime}=A^{\prime} O_{1}^{\prime}$
$\therefore O_{1}^{\prime} H^{\prime} / / O_{2}^{\prime} B^{\prime}$ ,四边形 $O_{1}^{\prime} O_{2}^{\prime} B^{\prime} H^{\prime}$ 是平行四边形

$\therefore O_{1}^{\prime} O_{2}^{\prime} / / H^{\prime} B^{\prime}$
$\because O_{1}^{\prime} O_{2}^{\prime} \perp O_{2} O_{2}^{\prime}, \quad O_{1}^{\prime} O_{2}^{\prime} \perp B^{\prime} O_{2}^{\prime}, \quad O_{2} O_{2}^{\prime} \cap B^{\prime} O_{2}^{\prime}=O_{2}^{\prime}$
$\therefore O_{1}^{\prime} O_{2}^{\prime} \perp$ 面 $O_{2} O_{2}^{\prime} B^{\prime} B$
$\therefore H^{\prime} B^{\prime} \perp$ 面 $O_{2} O_{2}{ }^{\prime} B^{\prime} B, \quad B O_{2}{ }^{\prime} \subset$ 面 $O_{2} O_{2}{ }^{\prime} B^{\prime} B$
$\therefore B O_{2}{ }^{\prime} \perp H^{\prime} B^{\prime}$
易知四边形 $A A^{\prime} H^{\prime} H$ 是正方形,且边长 $A A^{\prime}=2$
$\because \tan \angle H O_{1}^{\prime} H^{\prime}=\frac{H H^{\prime}}{O_{1}^{\prime} H^{\prime}}=2, \tan \angle A^{\prime} H^{\prime} G=\frac{A^{\prime} G}{A^{\prime} H^{\prime}}=\frac{1}{2}$
$\therefore \tan \angle H O_{1}^{\prime} H^{\prime} \cdot \tan \angle A^{\prime} H^{\prime} G=1$
$\therefore \angle H O_{1}^{\prime} H^{\prime}+\angle A^{\prime} H^{\prime} G=90^{\circ}$
$\therefore H O_{1}^{\prime} \perp H^{\prime} G$
易知 $O_{1}^{\prime} O_{2}^{\prime} / / H B$ ,四边形 $O_{1}^{\prime} O_{2}^{\prime} B H$ 是平行四边形
$\therefore B O_{2}{ }^{\prime} / / H O_{1}{ }^{\prime}$
$\therefore B O_{2}{ }^{\prime} \perp H^{\prime} G, \quad H^{\prime} G \bigcap H^{\prime} B^{\prime}=H^{\prime}$
$\therefore B O_{2}{ }^{\prime} \perp$ 平面 $H^{\prime} B^{\prime} G$.

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✅ 来源:2011年 · ?? · 2011_退役省自主命题 (2011·文) · 第 17 题 · 本题已通过人工审核与系统自动校验

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