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以动态角度审视空间位置与度量关系;重点是折叠过程中位置关系的变化,转动过程中度量关系的检测,学会用传统的逻辑推理来实现目标的达成;用向量的演绎推理来巧妙地转化;用坐标法来规范地探求几何量的大小.1.平面图形一次折叠成空间图形例1一张直角梯形纸片ABCD,AB=BC=2,AD=4,∠CBA一∠BAD=90°,如图1,沿对角线AC将△ABC折起,使点B在平面ACD内的射影O恰在AC上.
The relationship between spatial position and measurement is examined in a dynamic way. The emphasis is on the change of the positional relationship during the folding process, the detection of the metric relationship during the rotation process, the realization of the goal through traditional logical reasoning, the ingenious transformation with the deductive reasoning of vectors, Coordinate method to standardize the size of the geometric quantity .1 planar graphic folded into a spatial pattern example 1 a rectangular trapezoidal paper ABCD, AB = BC = 2, AD = 4, ∠CBA a ∠BAD = 90 °, As shown in FIG. 1, ABC is folded along diagonal AC so that the projection O of point B in plane ACD is just above AC.