# 空間中的平面與直線

the line is perpendicular to every line in the plane that passes through its foot
「垂直」是互相的，當直線垂直於平面，反過來也說平面垂直於直線：
When a line is perpendicular to a plane, the plane is also said to be perpendicular to the line.

Given a point and a plane, through the point pass a line perpendicular to the plane.

If a line is perpendicular to two different lines that lie in a plane and pass through its foot, then it's perpendicular to the plane.

HA、AB，和 CB

 [語音講解：plane.mp3]

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Created: Aug 9, 2022
Last Revised: 11/22,29