简明结论
先简单给出结论,我们考虑二维向量 x ⃗ = ( a , b ) , y ⃗ = ( c , d ) \vec{x}=(a,b),\vec{y}=(c,d) x
=(a,b),y
=(c,d) , 若
- x ⃗ × y ⃗ : = a × d − b × c = = 0 \vec{x}\times\vec{y}:=a\times d-b\times c==0 x
×y
:=a×d−b×c==0 , 则 两向量共线
- x ⃗ × y ⃗ : = a × d − b × c > 0 \vec{x}\times\vec{y}:=a\times d-b\times c>0 x
×y