Question

已知a=(2cosx,sinx),b=(cosx,sinx-√3cosx),设函数f(x)=a.b

Answer 1

f(x)=a*b

=2cos²x-sin²x-(√3)sinxcosx

=cos2x+(1/2)cos2x-(1/2)+((√3)/2)sin2x

=((√3)/2)sin2x+(3/2)cos2x-(1/2)

=(√3)sin(2x+(π/3))-(1/2)

对称轴

2x+(π/3)=kπ+(π/2)

x=(k/2)π+(π/12)