求数量积还是长度的乘积?(1)由向量BC=向量AD=(4,2)可知D(3,2)为AD中点,即E(1,1)向量EC=(2,-3)向量ED=(2,1)向量EC·向量ED=4-3=1(2)由(1)易知丨EC丨=√13丨ED丨=√5丨EC丨*丨ED丨=√65
