f(x)=2sin(wx-3.14/5)=-1
sin(wx-3.14/5)=-1/2=sin{w[x-3.14/(5w)]}
y=sin(x)与y=-1/2最近两个交点距离为(-3.14/6)-(3.14*5/6)=6.28/3
y=sin[x-3.14/(5w)]相当于y=sin(x)的左右平移.
y=sin[x-3.14/(5w)]与y=-1/2最近两个交点距离仍为6.28/3
y=sin(wx-3.14/5)相当与y=sin[x-3.14/(5w)]沿x轴方向伸缩至1/w倍,
则y=sin(wx-3.14/5)与y=-1/2最近两个交点距离为(1/w)*(6.28/3).
有(1/w)*(6.28/3)=3.14/3
w=2