π/(2w);
向量a×向量b=3sinwx*coswx-coswx^2=3/2sin2wx-1/2cos2wx-1/2;
f（x）=ab+1/2=3/2sin2wx-1/2cos2wx=sin(2wx-π/6);
T=2π/(2w)=π/w;对称轴距离=π/2w;