建立直角坐标系来解立体几何问题是非常有效的常用方法 ,但是往往要建立确定的坐标系 ,即 X轴、Y轴、Z轴和某一确定直线是重合的 ,其实有时并不需要每个坐标轴都要确定 .1　 “残缺”一个坐标轴例 1　在直三棱柱 ABC- A1B1C1中 AB1⊥ BC1,AB =CC1,求证 :AC1⊥ AB.证明　不妨设 It is very effective to establish a Cartesian coordinate system to solve the three-dimensional geometric problem. However, it is often necessary to establish a definite coordinate system. That is, the X-axis, Y-axis, and Z-axis are coincident with a certain straight line. In fact, sometimes it is not necessary to establish each coordinate. The axes must be determined. 1 “Incomplete” A coordinate axis Example 1 In the straight triangular prism ABC-A1B1C1 AB1 ⊥ BC1, AB = CC1, verification: AC1 ⊥ AB. The proof may be set