y=2cos(2x+π/4)
=2sin(π/2-2x-π/4)
=2sin(π/4-2x)
=-2sin(2x-π/4)
=-2sin[2(x-π/8)
把y的横坐标向左平移π/8得：y=-2sin[2(x-π/8+π/8)]=-2sin2x
√希望你能看懂,你能明白,赞同