f(x)=2cos^2x*sin^2x=1/2(sin2x)^2=(1-cos4x)/4
T=2π/w=π/2
f(-x)=(1-cos(-4x))/4=f(x)
即f(x)为偶函数 f(x)的最小周期为π/2cos4x=1-2(sin2x)^21-cos4x=2(sin2x)^2 =>1/2(sin2x)^2=(1-cos4x)/2这个就是二倍角公式啊