1.在平行四边形ABCD中,AC为对角线,若AB=(2,4) AC=(1,3) 则BD=?
问题描述：
1.在平行四边形ABCD中,AC为对角线,若AB=(2,4) AC=(1,3) 则BD=?
2.若a=(1,2) b=(x,1) u=a+2b v=2a-b 且u⊥v 求x的值
答
1. BD = AD - AB(向量的平行四边形加法法则:AC = AB + AD)= (AC - AB) - AB= AC - 2AB= (1, 3) - 2(2, 4)= (-3, -5)2. u = a + 2b = (1, 2) + 2(x, 1) = (1+2x, 4) v = 2...