y=cos(π/4+x)cos(π/4-x)+cos2x值域RT,
问题描述：
y=cos(π/4+x)cos(π/4-x)+cos2x值域
RT,
答
y=cos(π/4+x)cos(π/4-x)+cos2x
=cos(π/4+x)sin(x+π/4)+cos2x
=(1/2)sin(2x+π/2)+cos2x
=sin2x/2+cos2x
=√[(1/2)^2+1^2]sin(2x+θ)
=√5sin(2x+θ)/2
-√5/2