向量(a+3b)⊥(ka-b)可得到
(a+3b)与(ka-b)的数量积为0
(a+3b)×(ka-b)=
ka^2-ab+3kab-3b^2=0
a^2=4 b^2=16
ab=a·b·cos60°=4
可得4k-4+12k-48=0
16k=52
k=13/4
向量(a+3b)⊥(ka-b)可得到
(a+3b)与(ka-b)的数量积为0
(a+3b)×(ka-b)=
ka^2-ab+3kab-3b^2=0
a^2=4 b^2=16
ab=a·b·cos60°=4
可得4k-4+12k-48=0
16k=52
k=13/4