f(x)=cos(2X-π/3)+sin(x-π/4)sin(x+π/4)的最小正周期和图像的对称轴方程是什么?在【-π
2个回答

首先将f(x)化简

f(x)=cos(2X-π/3)+sin(x-π/4)sin(x+π/4)

=cos(2X-π/3)+1/2*(-cos(2x)+cos(-π/2))

=cos(2X-π/3)+1/2*(-cos(2x)+cos(-π/2))

=cos(2X-π/3)-1/2*cos(2x)

=cos(2X)cos(-π/3)-sin(2x)sin(-π/3)-1/2*cos(2x)

=1/2*cos(2X)+sin(2x)sin(π/3)-1/2*cos(2x)

=sin(2x)sin(π/3)

化简后可以看出sin(π/3)是常数,只要求出sin(2x)的值域即可.

可知当x∈【-π/12,π/2】时,2x∈【-π/6,π】

通过正弦函数曲线可知sin2x的最小值是-1/2,最大值是1

故f(x)的最小值是-1/2sin(π/3),最大值是sin(π/3)