f(x)=psinwx乘以coswx-（coswx）²（p＞0,w＞0）的最大值为0.5,最小正周期为0.5π

(1)..f(x)=(p/2)sin2wx-(1/2)cos2wx-1/2=(√(1+p²)/2)sin(2wx-b)-1/2,tanb=1/p,
2π/2w=π/2,w=2,
√(1+p²)/2-1/2=1/2,p=1
f(x)=(√2/2)sin(4x-π/4)-1/2
(2)余弦定理a²= b² + c² - 2bccosA=bc
整理1+2cosA=(b²+c²)/bc≥2
cosA≥1/2,0