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求异面直线所成的角例1如图1,正三棱锥S—ABC的侧棱与底面边长相等,如果E、F分别为SC、AB的中点,那么异面直线EF与SA所成的角
See Figure 1 for an example. As shown in Figure 1, the side edges of the regular triangular pyramid S-ABC are equal to the length of the bottom surface. If E and F are the mid-points of SC and AB respectively, The corner