2w=2π/π=2
w=1
f（π/8）=1/2sin（2Wx+2α）=1/2sin（π/4+2α）=1/4
sin（π/4+2α）=1/2
π/4+2α=π/6
a=-π/24 or a=23π/24可α是＞0小于π/2的π/4+2α=π-π/6a=7/24π