若3sina-根号3cosa=2根号3sin(a-b),-π/2

问题描述:

若3sina-根号3cosa=2根号3sin(a-b),-π/2

3sina-根号3cosa
=根号(3^2+3)cos(a+arctan(-根号3/3))
=2根号3cos(a-pai/6)
=2根号3sin(a-b)
,-π/2