【单选题】给出下列命题: ①直线l的方向向量为 a =(1,-1,2),直线m的方向向量为 b =(2,1, ),则l⊥m; ②直线l的方向向量为 a =(0,1,-1),平面α的法向量为 n =(1,-1,-1),l α,则l⊥α; ③平面α,β的法向量分别为 n 1 =(0,1,3), n 2 =(1,0,2),则α∥β; ④平面α经过三点A(1,0,-1),B(0,1,0),C(-1,2,0),向量 ...
【简答题】Fill in the blanks with win, defeat, or beat according to the context: 1) Our team was easily in the first of the competition. 2) The Americans the British in 1781. 3) They the war, although it cost t...