y=cos 2x
=sin (2x+π/2) .(诱导公式)
=sin [2(x+π/4)]
=sin [2(x+π/3)-π/6]
=sin [2(x+π/3-π/12)]
所以是由Y=sin(2X+π/3)沿X轴向右平移π/12个单位得到