f(x)=sin(2x+π/6)
=sin[(2x-π/3)+π/2]
=cos(2x-π/3)
=cos2(x-π/6)
y=cos(2x+π/4)
=cos2(x+π/8)
则π/8-(-π/6)=7π/24
即要将函数f(x)=sin(2x+π/6)的图像向左平移7π/24个单位可得到y= cos(2x+π/4)