y=sin(x+π/6)
向左平移π/3个单位 ==> y=sin(x+π/6+π/3)
图像上各点的横坐标压缩为原来的1/2 ==> y=sin(2(x+π/6+π/3))
y=sin(2(x+π/6+π/3)) ==> y=sin(2x+π)