Question

已知向量a=(sin x,1),向量b=(sinx,cosx+1/3) (0

Answer 1

[1].cosx+1/3=1,cosx=2/3,x=arxcos2/3.

[2].cos^2x=4/9,sin^2x=5/9,sinx=√5/3.

cos(2x+π/3)=cos2xcosπ/3-sin2xsinπ/3

=(2cos^2x-1)/2-√3sinxcosx

=-1/18-2√15/9.