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第三节平面向量的数量积及平面向量的应用举例 1.(2011·南京模拟)已知向量SKIPIF1<0=(1,2),SKIPIF1<0=(2,-3).若向量SKIPIF1<0满足(SKIPIF1<0+SKIPIF1<0)∥SKIPIF1<0,SKIPIF1<0⊥(SKIPIF1<0+SKIPIF1<0),则SKIPIF1<0=() A.(SKIPIF1<0,SKIPIF1<0)B.(-SKIPIF1<0,SKIPIF1<0)C.(SKIPIF1<0,SKIPIF1<0)D.(-SKIPIF1<0,-SKIPIF1<0) 2.(2010·湖南)若非零向量SKIPIF1<0,SKIPIF1<0满足|SKIPIF1<0|=|SKIPIF1<0|,(2SKIPIF1<0+SKIPIF1<0)·SKIPIF1<0=0,则SKIPIF1<0与SKIPIF1<0的夹角为() A.30°B.60°C.120°D.150° 3.已知下列命题中: (1)若k∈R,且kSKIPIF1<0=0,则k=0或SKIPIF1<0=SKIPIF1<0; (2)若SKIPIF1<0·SKIPIF1<0=0,则SKIPIF1<0=SKIPIF1<0或SKIPIF1<0=SKIPIF1<0; (3)若不平行的两个非零向量SKIPIF1<0,SKIPIF1<0,满足|SKIPIF1<0|=|SKIPIF1<0|,则(SKIPIF1<0+SKIPIF1<0)·(SKIPIF1<0-SKIPIF1<0)=0; (4)若SKIPIF1<0与SKIPIF1<0平行,则SKIPIF1<0·SKIPIF1<0=|SKIPIF1<0|·|SKIPIF1<0|. 其中真命题的个数是() A.0B.1C.2D.3 4.定义运算|SKIPIF1<0SKIPIF1<0SKIPIF1<0|=|SKIPIF1<0|·|SKIPIF1<0|·SKIPIF1<0,其中θ是向量SKIPIF1<0,SKIPIF1<0的夹角,若|SKIPIF1<0|=2,|SKIPIF1<0|=5,SKIPIF1<0·SKIPIF1<0=-6,则|SKIPIF1<0SKIPIF1<0SKIPIF1<0|=() A.8B.-8C.8或-8D.6 5.(2010·河北衡水中学仿真试卷)已知向量SKIPIF1<0=(1,1),SKIPIF1<0=(2,n),若|SKIPIF1<0+SKIPIF1<0|=SKIPIF1<0·SKIPIF1<0,则n为() A.-3B.-1C.1D.3 6.已知SKIPIF1<0=(2,1)与SKIPIF1<0=(1,2),要使|SKIPIF1<0+tSKIPIF1<0|最小,则实数t的值为SKIPIF1<0. 7.(2010·浙江)已知平面向量SKIPIF1<0,SKIPIF1<0,|SKIPIF1<0|=1,|SKIPIF1<0|=2,SKIPIF1<0⊥(SKIPIF1<0-2SKIPIF1<0),则|2SKIPIF1<0+SKIPIF1<0|的值是SKIPIF1<0. 8.已知SKIPIF1<0、SKIPIF1<0为互相垂直的单位向量,SKIPIF1<0=SKIPIF1<0-2SKIPIF1<0j,SKIPIF1<0=SKIPIF1<0+λSKIPIF1<0,且SKIPIF1<0与SKIPIF1<0的夹角为锐角,则实数λ的取值范围是SKIPIF1<0. 9.已知向量SKIPIF1<0=(SKIPIF1<0,1),SKIPIF1<0=(1,SKIPIF1<0),-SKIPIF1<0<θ<SKIPIF1<0. (1)若SKIPIF1<0⊥SKIPIF1<0,则θ=SKIPIF1<0; (2)|SKIPIF1<0+SKIPIF1<0|的最大值为.SKIPIF1<0 10.(2011·大连模拟)已知SKIPIF1<0,SKIPIF1<0,SKIPIF1<0是单位向量,且SKIPIF1<0·SKIPIF1<0=0,求(SKIPI