Question

非零向量a,b,| a•b |= |a |• |b|,求证a // b

Answer 1

a•b = |a| |b| cos t,t为夹角

| a•b |= |a |• |b|

=> ||a| |b| cos t| =|a |• |b|

=> |cost| =1 => t=0或者pi

所以平行