f(x)=sinxcosx-√3cos²x+√3/2(x∈R)
=1/2 sin2x-√3/2 (2cos²x-1)
=1/2 sin2x-√3/2 cos2x
=sin2xcosπ/3-sinπ/3cos2x
=sin(2x-π/3)
所以
(1)f(X) 的最小正周期=2π/2=π
(2)求f(x)的单调区间
增区间: 2kπ-π/2<2x-π/3< 2kπ+π/2
2kπ-π/6<2x< 2kπ+5π/6
kπ-π/12
减区间:2kπ+π/2<2x-π/3< 2kπ+3π/2
2kπ+5π/6<2x< 2kπ+11π/6
kπ+5π/12
(3)求f (x)图像的对称轴 ,对称中心
对称轴即sin(2x-π/3)=±1时,求出的x
2x-π/3=kπ+π/2
2x=kπ+5π/6
x=kπ/2+5π/12
对称中心:
横坐标即解sin(2x-π/3)=0时
2x-π/3=kπ
2x=kπ+π/3
x=kπ/2+π/6
即中心为(kπ/2+π/6,0)
初步估计你所写的表达式有问题!!!应该是:f(x)=sinx*cosx-√3cos²x+(√3/2)
f(x)=sinxcosx-√3cos²x+(√3/2)
=(1/2)sin2x-(√3/2)(2cos²x-1)
=(1/2)sin2x-(√3/2)cos2x
=sin[2x-(π/3)]
(1)最小正周期T=2π/2=π
(2)
当2x-(π/3)∈[2kπ-(π/2),2kπ+(π/2)]时单调递增
即,x∈[kπ-(π/12),kπ+(5π/12)](k∈Z)
当2x-(π/3)∈[2kπ+(π/2),2kπ+(3π/2)]时单调递减
即,x∈[kπ+(5π/12),kπ+(11π/12)](k∈Z)
(3)
当2x-(π/3)=kπ+(π/2),即x=(kπ/2)+(5π/12)(k∈Z)时为对称轴;
当2x-(π/3)=kπ,即x=(kπ/2)+(π/6)(k∈Z)时为对称中心。