y=sinx ;x→x-π/6(即右移π/6个单位)得 y=sin(x-π/6);
x→2x(即每点横坐标缩短为原来的1/2)得y=sin(2x-π/6);
再将纵坐标拉伸为原来的2倍得y=2sin(2x-π/6);