已知sin(π/2 +a)=12/13(-π/2<a<0),求cos(a-π/6)的值,

问题描述:

已知sin(π/2 +a)=12/13(-π/2<a<0),求cos(a-π/6)的值,

sin(π/2+a)=cos(a)=12/13
cos(a)=12/13
因为(-π/2