已知A、B、C三点在球心为O的球面上，AB=AC=2，∠BAC=90°，球心O到

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问题填空题

已知A、B、C三点在球心为O的球面上，AB=AC=2，∠BAC=90°，球心O到平面ABC的距离为

，则球O的表面积为______．

答案

由已知中AB=AC=2，∠BAC=90°，

我们可得BC为平面ABC截球所得截面的直径

即2r=

AB2+AC2

∴r=

又∵球心到平面ABC的距离d=

∴球的半径R=

r2+d2

∴球的表面积S=4π?R²=16π

故答案为：16π．

填空题

用适当的介词填空。

1. The writer was educated _____ a very good school.

2. He received a title _____ a reward for his service to the na- tion.

3. She rewarded the boy with＄10_____ his help.

4. They stopped me _____ going out of the door.

5. The teacher refused to have his daughter in his class, for fear _____ showing favor to her.

名词解释

可变组成指数