已知向量a=(cosa,sina),向量b=(cosβ,sinβ),若-π/4<a<π/4,β=π/4,且且a点乘b=3/5,求sina
问题描述:
已知向量a=(cosa,sina),向量b=(cosβ,sinβ),若-π/4<a<π/4,β=π/4,且且a点乘b=3/5,求sina
答
a*b=cosacosβ+sinasinβ=cos(a-β)=3/5
-π/4<a<π/4,β=π/4,所以:-π/2